WILLIAM BLAIR MUTUAL FUNDS INC
485APOS, 1999-07-30
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<PAGE>   1

As filed with the Securities and Exchange Commission on or about July 30, 1999

                                          Registration No. 33-17463 and 811-5344
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                               ------------------


                                    FORM N-1A
             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                        Pre-Effective Amendment No. ____


                        Post-Effective Amendment No. 20                  [X]

                                     and/or

                             REGISTRATION STATEMENT
                    Under the Investment Company Act of 1940

                                 AMENDMENT NO. 21                        [X]


                        WILLIAM BLAIR MUTUAL FUNDS, INC.
               (Exact Name of Registrant as Specified in Charter)

                              222 WEST ADAMS STREET
                             CHICAGO, ILLINOIS 60606
          (Address of Principal Executive Offices, including Zip Code)

       Registrant's Telephone Number, Including Area Code: (312) 364-8000

                                    Copy to:


             MARCO HANIG                              CATHY G. O'KELLY
        222 WEST ADAMS STREET                  VEDDER, PRICE, KAUFMAN & KAMMHOLZ
       CHICAGO, ILLINOIS 60606                     222 NORTH LASALLE STREET
(Name and Address of Agent for Service)            CHICAGO, ILLINOIS 60601

It is proposed that this filing will become effective (check appropriate box)

[ ] immediately upon filing pursuant to paragraph (b); or
[ ] on (date) pursuant to paragraph (b); or
[ ] 60 days after filing pursuant to paragraph (a)(1); or
[X] on September 30, 1999 pursuant to paragraph (a)(1); or
[ ] 75 days after filing pursuant to paragraph (a)(2); or
[ ] on (date) pursuant to paragraph (a)(2) of Rule 485.

If appropriate, check the following box:

[ ] this post-effective amendment designates a new effective date for a
previously filed post-effective amendment.

================================================================================


<PAGE>   2


R CLASS PROSPECTUS
May 1, 1999, as supplemented September 30, 1999.



                        WILLIAM BLAIR MUTUAL FUNDS, INC.



               GROWTH FUND

               VALUE DISCOVERY FUND

               INTERNATIONAL GROWTH FUND

               EMERGING MARKETS GROWTH FUND

               INCOME FUND

               READY RESERVES FUND


This prospectus contains important information about each Fund, including their
investment objectives. For your benefit and protection, please read it before
you invest and keep it for future reference. This prospectus relates only to
Class R Shares of each Fund, except for the Ready Reserves Fund which only has a
single class of shares.













THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE
SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO
THE CONTRARY IS A CRIMINAL OFFENSE.





                        WILLIAM BLAIR MUTUAL FUNDS, INC.
                        222 West Adams Street
                        Chicago, Illinois 60606




<PAGE>   3

TABLE OF CONTENTS


<TABLE>
<S>                                                                                <C>
SUMMARY............................................................................ 1
         Growth Fund............................................................... 1
         Value Discovery Fund...................................................... 3
         International Growth Fund................................................. 6
         Emerging Markets Growth Fund.............................................. 9
         Income Fund.............................................................. 11
         Ready Reserves Fund...................................................... 13

INVESTMENT OBJECTIVES, PRINCIPAL INVESTMENT STRATEGIES AND RISKS.................. 15
         Growth Fund.............................................................. 16
         Value Discovery Fund..................................................... 18
         International Growth Fund................................................ 20
         Emerging Markets Growth Fund............................................. 23
         Income Fund.............................................................. 27
         Ready Reserves Fund...................................................... 29

MANAGEMENT OF THE FUNDS........................................................... 31

YOUR ACCOUNT...................................................................... 33
         R Class Shares........................................................... 33
         How to Buy Shares........................................................ 33
         How to Sell Shares....................................................... 34
         How to Exchange Shares................................................... 38
         Dividends and Distributions.............................................. 38
         Taxes.................................................................... 39

DETERMINATION OF NET ASSET VALUE.................................................. 40

SHAREHOLDER SERVICES AND ACCOUNT POLICIES......................................... 41

INVESTMENT GLOSSARY............................................................... 44

FOR MORE INFORMATION.....................................................  Back Cover
</TABLE>




<PAGE>   4
WILLIAM BLAIR GROWTH FUND                                                SUMMARY
- --------------------------------------------------------------------------------

INVESTMENT OBJECTIVE: The William Blair Growth Fund seeks long-term appreciation
of capital by investing in well-managed companies in growing industries.

MAIN INVESTMENT STRATEGIES: The Fund invests primarily in a diversified
portfolio of common stocks of domestic companies. The Adviser seeks growth
opportunities by investing in large, medium and small companies in varying
proportions. With respect to large companies, the Adviser looks for high
quality, seasoned growth companies that have demonstrated sustained growth over
a long period of time. With respect to medium-sized companies, the Adviser
searches for companies that are generally of similar investment quality to large
companies but whose records of sales and earnings growth are not as well
established. With respect to small companies, the Adviser looks for emerging,
rapid growth companies that have had especially vigorous growth in revenues and
earnings. The Fund is designed for long-term investors.

MAIN RISKS OF INVESTING: Since the Fund invests most of its assets in common
stocks, the primary risk is that the value of the stocks it holds might decrease
in response to the activities of an individual company or general economic and
market conditions. If this occurs, the Fund's net asset value may also decrease.
The securities of small and medium size companies may be more volatile and more
speculative than the securities of larger, more established issuers. In
addition, small and medium companies may be traded in low volumes, which can
increase volatility. Of course, the skill of the Adviser will play a significant
role in the Fund's ability to achieve its investment objective. The Fund's
returns will vary, and you could lose money by investing in the Fund.


FUND PERFORMANCE HISTORY



ANNUAL TOTAL RETURNS. The bar chart below provides an illustration of how the
Fund's performance has varied in each of the last 10 calendar years. The Fund's
past performance does not necessarily indicate how it will perform in the
future.


<TABLE>
<CAPTION>
YEAR             PERCENT
- ----             -------
<S>              <C>
1989              30.45
1990              (2.02)
1991              44.37
1992               7.61
1993              15.51
1994               6.45
1995              29.07
1996              17.99
1997              20.07
1998              27.15
</TABLE>


HIGHEST AND LOWEST QUARTERLY RETURNS. During the period shown in the bar chart,
the highest return for a quarter was 23.69% (fourth quarter 1998) and the lowest
return for a quarter was -14.61% (third quarter 1990). Shareholders should be
aware that the Fund is a long-term investment and is not managed for short-term
results.



AVERAGE ANNUAL TOTAL RETURNS. The following table compares the Fund's average
annual returns for the periods ended December 31, 1998, to a broad-based market
benchmark.


<TABLE>
<CAPTION>
                     1 YEAR      5 YEARS    10 YEARS
                     ------      -------    --------
<S>                  <C>         <C>        <C>
Growth Fund           27.15%      19.87%     18.96%
S&P 500*              28.57%      24.06%     19.21%
</TABLE>


- ----------
* The Standard and Poor's 500 Stock Index generally represents broad larger
  capitalization equity market performance.




<PAGE>   5



FEES AND EXPENSES: This section describes the fees and expenses that you may pay
if you buy and hold Class R shares of the Fund.



SHAREHOLDER FEES. William Blair Mutual Fund Class R shares are no-load
investments, so you will not pay shareholder fees to buy shares, reinvest
dividends in additional shares or exchange into the Class R shares of another
Fund. However, in order to discourage short-term trading, the Fund may charge a
redemption fee of 1% of the value of the shares sold within 180 days of their
purchase. This redemption fee will be retained by the Fund. The Fund discourages
short-term investments in the Fund because they have a negative impact on
remaining shareholders.




<TABLE>
<CAPTION>
                                                          REDEMPTION FEE
                                                          --------------
<S>                                                       <C>
Shares held less than 180 days..........................       1.0%
Shares held 180 days or more............................       None
</TABLE>


ANNUAL FUND OPERATING EXPENSES are paid out of the Fund's assets and include
fees for portfolio management, maintenance of shareholder accounts, shareholder
servicing, accounting and other services. You do not pay these fees directly
but, as the example shows, these costs are borne indirectly by shareholders.


<TABLE>
<CAPTION>
  ANNUAL FUND OPERATING EXPENSES (expenses that are deducted from Fund assets)
<S>                                                                   <C>
Management Fee..................................................       .75%
Distribution (Rule 12b-1) Fee...................................      None(1)
Other Expenses..................................................       .09%
      Total Annual Fund Operating Expenses......................       .84%
</TABLE>



- -----------
(1)  The Fund's Board of Directors has approved a shareholder solicitation
     regarding a proposed .25% distribution fee. The proposal is scheduled to be
     voted upon by shareholder of record on , 1999 at a meeting on November 30,
     1999.



EXAMPLE: This example is intended to help you compare the cost of investing in
Class R shares of the Fund with the cost of investing in other mutual funds. The
example assumes that you: invest $10,000 in the Fund, redeem all of your shares
at the end of the periods shown, earn a 5% return each year and incur the same
operating expenses as shown above:




<TABLE>
<CAPTION>
   1 YEAR      3 YEARS     5 YEARS    10 YEARS
   ------      -------     -------    --------
<S>            <C>         <C>        <C>
    $86         $269        $468       $1,040
</TABLE>


FINANCIAL HIGHLIGHTS: The table below is intended to help you understand the
Fund's financial performance for the past several years. The total return
figures show what an investor in the Fund would have earned (or lost) assuming
reinvestment of all dividends and distributions. This information has been
audited by Ernst & Young LLP, whose report, along with the Fund's financial
statement, is included in the annual report, which is available upon request
(see back cover).



<TABLE>
<CAPTION>
                                                                                  YEARS ENDED DECEMBER 31
                                                        ---------------------------------------------------------------------------
                                                            1998             1997           1996            1995           1994
                                                        ------------    ------------    ------------    ------------   ------------
<S>                                                     <C>             <C>             <C>             <C>            <C>
Net asset value, beginning of year .................... $     15.350    $     13.480    $     11.900    $      9.600   $      9.730
Income from investment operations:
   Net investment income (loss) .......................        (.003)          (.023)          (.010)           .034           .027
   Net realized and unrealized gain on investments ....        4.123           2.694           2.144           2.750           .581
                                                        ------------    ------------    ------------    ------------   ------------
Total from investment operations ......................        4.120           2.671           2.134           2.784           .608
Less distributions from:
   Net investment income ..............................           --              --            .010            .030           .025
   Net realized gain on investments ...................        1.500            .801            .544            .454           .713
                                                        ------------    ------------    ------------    ------------   ------------
Total distributions ...................................        1.500            .801            .554            .484           .738
                                                        ------------    ------------    ------------    ------------   ------------
Net asset value, end of year .......................... $     17.970    $     15.350    $     13.480    $     11.900   $      9.600
                                                        ============    ============    ============    ============   ============

Total return (%) ......................................        27.15           20.07           17.99           29.07           6.45
Ratios to average net assets (%):
   Expenses ...........................................          .84             .84             .79             .65            .71
   Net investment income (loss) .......................         (.02)           (.16)           (.08)            .34            .32
Supplemental data:
   Net assets at end of year (000s) ................... $    742,056    $    591,353    $    501,774    $    363,036   $    217,560
   Portfolio turnover rate (%) ........................           37              34              43              32             46
</TABLE>




                                       2
<PAGE>   6

WILLIAM BLAIR VALUE DISCOVERY FUND                                       SUMMARY
- --------------------------------------------------------------------------------


INVESTMENT OBJECTIVE: The William Blair Value Discovery Fund seeks long-term
capital appreciation.

MAIN INVESTMENT STRATEGIES: The Fund invests primarily in a diversified
portfolio of the equity securities of small companies that the Adviser believes
offer a long-term investment value. In implementing its value discipline, the
Adviser evaluates the extent to which a company meets the following criteria:
(a) whether the company's current market value reflects a material discount from
the Adviser's estimate of the company's value, (b) whether the company has a
reasonable expectation of improving its level of profitability over a three-year
investment horizon, (c) whether the company has a capable and skilled management
team, (d) whether the company has a relatively strong capital structure, and (e)
whether there is a likelihood that the company will undergo a positive corporate
change within a three-year investment horizon. The weight that the Adviser gives
to each of the investment criteria depends upon the circumstances, and some of
the Fund's investments will not meet all of the criteria. The Fund is designed
for long-term investors.

MAIN RISKS OF INVESTING: Since the Fund invests most of its assets in equity
securities, the primary risk is that the value of the securities it holds might
decrease in response to the activities of an individual company or general
economic and market conditions. If this occurs, the Fund's net asset value may
also decrease. The securities of smaller companies may be more volatile and more
speculative than the securities of larger, more established issuers, which may
cause the Fund's share price to be more volatile. In addition, small companies
may be traded in low volumes. This can increase volatility and increase the risk
that the Fund will not be able to sell the security on short notice at a
reasonable price. Of course, the skill of the Adviser will play a significant
role in the Fund's ability to achieve its investment objective. The Fund's
returns will vary, and you could lose money by investing in the Fund.


FUND PERFORMANCE HISTORY



ANNUAL TOTAL RETURNS. The bar chart to the right provides an illustration of how
the Fund's performance has varied in each of the calendar years since the Fund
started. The Fund's past performance does not necessarily indicate how it will
perform in the future.


<TABLE>
<CAPTION>
YEAR             PERCENT
- ----             -------
<S>              <C>
1997              33.46
1998               0.66
</TABLE>


HIGHEST AND LOWEST QUARTERLY RETURNS. During the period shown in the bar chart,
the highest return for a quarter was 26.58% (quarter ended 9/30/97) and the
lowest return for a quarter was -17.59% (quarter ended 9/30/98). Shareholders
should be aware that the Fund is a long-term investment and is not managed for
short-term results.



AVERAGE ANNUAL TOTAL RETURNS. The following table compares the Fund's average
annual returns for the periods ended December 31, 1998, indicated to a
broad-based securities market index.




<TABLE>
<CAPTION>
                             1 YEAR        LIFE OF FUND**
                             ------        --------------
<S>                          <C>           <C>
Value Discovery Fund          0.66%            15.91%
Russell 2000 Index*          (2.55)%            9.20%
</TABLE>



- ----------
*    The Russell 2000 Index is a composite of the smallest 2000 stocks of the
     Russell 3000 Index, which consists of the largest 3000 stocks in the U.S.
     market as determined by market capitalization.
**   The Fund's inception was on December 23, 1996.




                                       3
<PAGE>   7




FEES AND EXPENSES: This section describes the fees and expenses that you may pay
if you buy and hold Class R shares of the Fund.



SHAREHOLDER FEES. William Blair Mutual Fund Class R shares are no-load
investments, so you will not pay shareholder fees to buy shares, reinvest
dividends in additional shares or exchange into the Class R shares of another
Fund. However, in order to discourage short-term trading, the Fund may charge a
redemption fee of 1% of the value of the shares sold within 180 days of their
purchase. This redemption fee will be retained by the Fund. The Fund discourages
short-term investments in the Fund because they have a negative impact on
remaining shareholders.



<TABLE>
<CAPTION>

                                                              REDEMPTION FEE
                                                              --------------
<S>                                                           <C>
Shares held less than 180 days.............................         1.0%
Shares held 180 days or more...............................         None
</TABLE>


ANNUAL FUND OPERATING EXPENSES are paid out of the Fund's assets and include
fees for portfolio management, maintenance of shareholder accounts, shareholder
servicing, accounting and other services. You do not pay these fees directly
but, as the example shows, these costs are borne indirectly by shareholders.

  ANNUAL FUND OPERATING EXPENSES (expenses that are deducted from Fund assets)


<TABLE>
<S>                                                                <C>
Management Fee...................................................   1.15%
Distribution (Rule 12b-1) Fee....................................   None(1)
Other Expenses...................................................    .37%
                                                                    ----
     Total Annual Fund Operating Expenses........................   1.52%
</TABLE>



- ------------
(1)  The Fund's Board of Directors has approved a shareholder solicitation
     regarding a proposed .25% distribution fee. The proposal is scheduled to be
     voted upon by shareholder of record on , 1999 at a meeting on November 30,
     1999.



EXAMPLE: This example is intended to help you compare the cost of investing in
Class R shares of the Fund with the cost of investing in other mutual funds. The
example assumes that you: invest $10,000 in the Fund, redeem all of your shares
at the end of the periods shown, earn a 5% return each year and incur the same
operating expenses as shown above:




<TABLE>
<CAPTION>
1 YEAR      3 YEARS     5 YEARS    10 YEARS
- ------      -------     -------    --------
<S>         <C>         <C>        <C>
$156        $484         $835       $1,823
</TABLE>


FINANCIAL HIGHLIGHTS: The table below is intended to help you understand the
Fund's financial performance for the past several years. The total return
figures show what an investor in the Fund would have earned (or lost) assuming
reinvestment of all dividends and distributions. This information has been
audited by Ernst & Young LLP, whose report, along with the Fund's financial
statement, is included in the annual report, which is available upon request
(see back cover).



                                       4
<PAGE>   8



<TABLE>
<CAPTION>
                                                                           YEARS ENDED DECEMBER 31
                                                                 -------------------------------------------
                                                                     1998           1997            1996(a)
                                                                 -----------    -----------      -----------
<S>                                                              <C>            <C>              <C>
Net asset value, beginning of year ...........................   $    12.970    $    10.000      $    10.000
Income from investment operations:
  Net investment income ......................................          .088           .029               --
  Net realized and unrealized gain (loss) on investments .....         (.005)         3.305               --
                                                                 -----------    -----------      -----------
Total from investment operations .............................          .083          3.334               --
Less distributions from:
  Net investment income ......................................          .093           .020               --
  Net realized gain on investments ...........................            --           .344               --
                                                                 -----------    -----------      -----------
Total distributions ..........................................          .093           .364               --
                                                                 -----------    -----------      -----------
Net asset value, end of year .................................   $    12.960    $    12.970      $    10.000
                                                                 ===========    ===========      ===========
Total return (%) .............................................          0.66          33.46               --
Ratios to average net assets (%):
  Expenses ...................................................          1.52           1.50(b)            --
  Net investment income ......................................           .76            .29(b)            --
Supplemental data:
  Net assets at end of year (000s) ...........................   $    44,675    $    30,354      $         2
  Portfolio turnover rate (%) ................................            78             69               --
</TABLE>




- ------------
(a)  For the period December 23, 1996 (Commencement of Operations) to December
     31, 1996.
(b)  Without the waiver of expenses in 1997, the expense ratio would have been
     1.78% and the net investment income ratio would have been .016%.




                                       5
<PAGE>   9

WILLIAM BLAIR INTERNATIONAL GROWTH FUND                                  SUMMARY
- --------------------------------------------------------------------------------

INVESTMENT OBJECTIVE: The William Blair International Growth Fund seeks
long-term capital appreciation through investment in well-managed, quality
growth companies.

MAIN INVESTMENT STRATEGIES: The Fund invests primarily in a diversified
portfolio of common stocks of foreign companies of all sizes. In choosing
investments, the Adviser performs fundamental company analysis. The Adviser
generally seeks common stocks of companies that historically have had and are
expected to maintain superior growth, profitability and quality relative to
local markets and relative to companies within the same industry worldwide.
Following stock selection, country selection and industry allocation are the
next most important investment criteria. The Adviser will vary the geographic
diversification and types of securities in which the Fund invests based upon its
continuous evaluation of economic, market and political trends throughout the
world. The Adviser normally will allocate the Fund's investments among at least
six different countries. Normally, the Fund's investments will be divided among
Continental Europe, the United Kingdom, Canada, Japan and the markets of the
Pacific Basin. However, selective investments may also be made in Latin America
and in emerging markets, which include every country in the world except the
United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and
most Western European countries. The Fund is designed for long-term investors.

MAIN RISKS OF INVESTING: Because the Fund invests most of its assets in common
stocks, the primary risk is that the value of the stocks it holds might decrease
in response to the activities of those companies or market and economic
conditions. If this occurs, the Fund's net asset value may also decrease.
Foreign investments often involve additional risks, including political
instability, differences in financial reporting standards, and less stringent
regulation of securities markets. These risks are magnified in less-established,
emerging markets. Because the securities held by the Fund usually will be
denominated in currencies other than the U.S. dollar, changes in foreign
currency exchange rates may adversely affect the value of the Fund's
investments. In addition, the Fund may invest in the securities of small
companies, which may be more volatile and less liquid than securities of large
companies. Of course, the skill of the Adviser will play a significant role in
the Fund's ability to achieve its investment objective. The Fund's returns will
vary, and you could lose money by investing in the Fund.


FUND PERFORMANCE HISTORY



ANNUAL TOTAL RETURNS. The bar chart to the right provides an illustration of how
the Fund's performance has varied in each calendar year since the Fund started.
The Fund's past performance does not necessarily indicate how it will perform in
the future.


<TABLE>
<CAPTION>
YEAR             PERCENT
- ----             -------
<S>              <C>
1993              33.65
1994              (0.04)
1995               7.22
1996              10.20
1997               8.39
1998              11.46
</TABLE>


HIGHEST AND LOWEST QUARTERLY RETURNS. During the period shown in the bar chart,
the highest return for a quarter was 17.43% (quarter ended 3/31/98) and the
lowest return for a quarter was -16.70% (quarter ended 9/30/98). Shareholders
should be aware that the Fund is a long-term investment and is not managed for
short-term results.



AVERAGE ANNUAL TOTAL RETURNS. The table compares the Fund's average annual total
returns for the periods indicated to a broad-based securities market index.




<TABLE>
<CAPTION>
                                         1 YEAR     5 YEARS      LIFE OF FUND**
                                         ------     -------      ---------------
<S>                                      <C>        <C>          <C>
International Growth Fund                11.46%      7.37%           11.10%
Morgan Stanley Int'l Index*              14.46%      7.87%           10.91%
</TABLE>



- ----------------
*    The Morgan Stanley Capital International All Country World Free except U.S.
     Index includes developed and emerging markets and reduces the Japanese
     portion, making it comparable to the International Growth Fund in terms of
     investment approach.
**   The Fund's inception was on October 1, 1992.




                                       6
<PAGE>   10





FEES AND EXPENSES: This section describes the fees and expenses that you may pay
if you buy and hold Class R shares of the Fund.



SHAREHOLDER FEES. William Blair Mutual Fund Class R shares are no-load
investments, so you will not pay shareholder fees to buy shares, reinvest
dividends in additional shares or exchange into the Class R shares of another
Fund. However, in order to discourage short-term trading, the Fund may charge a
redemption fee of 1% of the value of the shares sold within 180 days of their
purchase. This redemption fee will be retained by the Fund. The Fund discourages
short-term investments in the Fund because they have a negative impact on
remaining shareholders.




<TABLE>
<CAPTION>
                                                                  REDEMPTION FEE
                                                                  --------------
<S>                                                               <C>
Shares held less than 180 days................................          1.0%
Shares held 180 days or more..................................         None
</TABLE>


ANNUAL FUND OPERATING EXPENSES are paid out of the Fund's assets and include
fees for portfolio management, maintenance of shareholder accounts, shareholder
servicing, accounting and other services. You do not pay these fees directly
but, as the example shows, these costs are borne indirectly by shareholders.

  ANNUAL FUND OPERATING EXPENSES (expenses that are deducted from Fund assets)


<TABLE>
<S>                                                                   <C>
Management Fee.....................................................   1.10%
Distribution (Rule 12b-1) Fee......................................   None(1)
Other Expenses.....................................................     26%
                                                                      ----
         Total Annual Fund Operating Expenses......................   1.36%
</TABLE>



- -----------
(1)  The Fund's Board of Directors has approved a shareholder solicitation
     regarding a proposed .25% distribution fee. The proposal is scheduled to be
     voted upon by shareholder of record on , 1999 at a meeting on November 30,
     1999.



EXAMPLE: This example is intended to help you compare the cost of investing in
Class R shares of the Fund with the cost of investing in other mutual funds. The
example assumes that you: invest $10,000 in the Fund, redeem all of your shares
at the end of the periods shown, earn a 5% return each year and incur the same
operating expenses as shown above:




<TABLE>
<CAPTION>
1 YEAR      3 YEARS     5 YEARS    10 YEARS
- ------      -------     -------    --------
<S>          <C>         <C>        <C>
 $139        $433        $749       $1,643
</TABLE>


FINANCIAL HIGHLIGHTS: The table below is intended to help you understand the
Fund's financial performance for the past several years. The total return
figures show what an investor in the Fund would have earned (or lost) assuming
reinvestment of all dividends and distributions. This information has been
audited by Ernst & Young LLP, whose report, along with the Fund's financial
statement, is included in the annual report, which is available upon request
(see back cover).



                                       7
<PAGE>   11





<TABLE>
<CAPTION>
                                                                                YEARS ENDED DECEMBER 31
                                                          -----------------------------------------------------------------
                                                             1998          1997          1996          1995          1994
                                                          ---------      --------      --------      --------      --------
<S>                                                       <C>            <C>           <C>           <C>           <C>
Net asset value, beginning of year ....................   $  13.140      $ 13.950      $ 13.120      $ 12.360      $ 13.180
Income from investment operations:
  Net investment income ...............................        .074          .072          .029          .105          .016
  Net realized and unrealized gain (loss) on
    investments, foreign currency and other assets
    and liabilities ...................................       1.431         1.056         1.299          .785         (.025)
                                                          ---------      --------      --------      --------      --------
Total from investment operations ......................       1.505         1.128         1.328          .890         (.009)
Less distributions from:
  Net investment income ...............................        .024(a)       .078(a)       .068(a)       .130(a)       .024
  Net realized gain on investments ....................        .001         1.860          .430            --          .714
Tax return of capital .................................          --            --            --            --          .073(b)
                                                          ---------      --------      --------      --------      --------
Total distributions ...................................        .025         1.938          .498          .130          .811
                                                          ---------      --------      --------      --------      --------
Net asset value, end of year ..........................   $  14.620      $ 13.140      $ 13.950      $ 13.120      $ 12.360
                                                          =========      ========      ========      ========      ========
Total return (%) ......................................       11.46          8.39         10.20          7.22          (.04)
Ratios to average net assets (%):
  Expenses ............................................        1.36          1.43          1.44          1.48          1.51
  Net investment income ...............................         .09           .01           .19           .87           .15
Supplemental data:
  Net assets at end of year (000s) ....................   $ 139,746      $128,747      $105,148      $ 89,762      $ 70,403
  Portfolio turnover rate (%) .........................          98           102            89            77            40
</TABLE>


- --------------
(a)  Includes $.024, $.078, $.022 and $.061 in passive foreign investment
     company transactions which are treated as ordinary income for Federal
     income tax purposes for 1998, 1997, 1996 and 1995, respectively.
(b)  Includes $431 relating to a tax return of capital.



                                       8
<PAGE>   12

WILLIAM BLAIR EMERGING MARKETS GROWTH FUND                               SUMMARY
- --------------------------------------------------------------------------------

INVESTMENT OBJECTIVE: The William Blair Emerging Markets Growth Fund seeks
long-term capital appreciation.

MAIN INVESTMENT STRATEGIES: The Fund invests primarily in a diversified
portfolio of equity securities issued by companies in emerging markets. In
choosing investments, the Adviser first analyzes individual companies. The
Adviser generally seeks well-managed companies with superior business
fundamentals, including global leadership in product quality or cost
competitiveness, dominant or improving market position within a growing local or
regional economy, and sustainable above-average and/or increasing returns on
invested capital. Following stock selection, the Adviser allocates investments
based upon its analysis of the economic strength of various countries and
industries. The Adviser normally will allocate the Fund's investments among at
least six different countries. Currently, emerging markets include every country
in the world other than the United States, Canada, Japan, Australia, New
Zealand, Hong Kong, Singapore and most Western European countries. The Fund is
designed for long-term investors.

MAIN RISKS OF INVESTING: Because the Fund invests most of its assets in equity
securities of companies, the primary risk is that value of the securities it
holds might decrease in response to the activities of those companies or markets
and economic conditions. If this occurs, the Fund's net asset value may also
decrease. Foreign investments often involve additional risks, such as political
instability, differences in financial reporting standards and less stringent
regulation of securities markets. These risks may be greatly increased in
emerging market countries because the securities in emerging markets may be
subject to greater volatility and less liquidity than companies in more
developed markets. Because the securities held by the Fund usually will be
denominated in currencies other than the U.S. dollar, changes in foreign
currency exchange rates may adversely affect the value of the Fund's
investments. The currencies of certain emerging market countries have
experienced a steady devaluation relative to the U.S. dollar, and continued
devaluations may adversely affect the value of the Fund's assets denominated in
such currencies. Many emerging markets have experienced substantial rates of
inflation for many years, and continued inflation may adversely affect the
economies and securities markets of such countries. The Fund also may invest in
the securities of small companies, which may be more volatile and less liquid
than securities of large companies. Of course, the skill of the Adviser will
play a significant role in the Fund's ability to achieve its investment
objective. The Fund's returns will vary, and you could lose money by investing
in the Fund.


FEES AND EXPENSES: This section describes the fees and expenses that you may pay
if you buy and hold Class R shares of the Fund.



SHAREHOLDER FEES. William Blair Mutual Fund Class R shares are no-load
investments, so you will not pay shareholder fees to buy shares, reinvest
dividends in additional shares or exchange into the Class R shares of another
Fund. However, in order to discourage short-term trading, the Fund may charge a
redemption fee of 1% of the value of the shares sold within 180 days of their
purchase. This redemption fee will be retained by the Fund. The Fund discourages
short-term investments in the Fund because they have a negative impact on
remaining shareholders.




<TABLE>
<CAPTION>
                                                    REDEMPTION FEE
                                                    --------------
<S>                                                 <C>
Shares held less than 180 days.................          1.0%
Shares held 180 days or more...................          None
</TABLE>


ANNUAL FUND OPERATING EXPENSES are paid out of the Fund's assets and include
fees for portfolio management, maintenance of shareholder accounts, shareholder
servicing, accounting and other services. You do not pay these fees directly
but, as the example shows, these costs are borne indirectly by shareholders.



                                       9
<PAGE>   13



  ANNUAL FUND OPERATING EXPENSES (expenses that are deducted from Fund assets)

<TABLE>
<S>                                                                       <C>
Management Fee.......................................................    1.40%
Distribution (Rule 12b-1) Fee........................................    None*
Other Expenses.......................................................    4.95%
                                                                         ----
         Total Annual Fund Operating Expenses (without waiver).......    6.35%**
               Adviser's Voluntary Expense Waiver....................   -4.10%
                                                                         ----
                  Total Annual Operating Expenses (with waiver)......    2.25%
</TABLE>



- ------------
*    The Fund's Board of Directors has approved a shareholder solicitation
     regarding a proposed .25% distribution fee. The proposal is scheduled to be
     voted upon by shareholder of record on , 1999 at a meeting on November 30,
     1999.
**   Due to the Adviser voluntarily waiving fees and absorbing expenses, the
     Fund's actual total expenses were 2.25% (annualized) during 1998. The
     Adviser intends to voluntarily cap the Fund's expenses at 2.25%
     indefinitely.



EXAMPLE: This example is intended to help you compare the cost of investing in
Class R shares of the Fund with the cost of investing in other mutual funds. The
example assumes that you: invest $10,000 in the Fund, redeem all of your shares
at the end of the periods shown, earn a 5% return each year and incur the same
operating expenses as shown above:




<TABLE>
<CAPTION>
                             1 YEAR     3 YEARS       5 YEARS      10 YEARS
                             ------     -------       -------      --------
<S>                           <C>       <C>           <C>           <C>
Without expense cap*:         $651      $1,923        $3,158        $6,084
</TABLE>



- -----------
*    With the expense cap, the Fund's operating expenses would be as follows: 1
     Year: $231; 3 Years: $711; 5 Years: $1,217; 10 Years: $2,607.


FINANCIAL HIGHLIGHTS: The table below is intended to help you understand the
Fund's financial performance since the commencement of its operations. The total
return figures show what an investor in the Fund would have earned (or lost)
assuming reinvestment of all dividends and distributions. This information has
been audited by Ernst & Young LLP, whose report, along with the Fund's financial
statement, is included in the annual report, which is available upon request
(see back cover).



<TABLE>
<CAPTION>
                                                                    YEAR ENDED DECEMBER 31
                                                                    ----------------------
                                                                          1998(a)(b)
                                                                    ----------------------
<S>                                                                        <C>
Net asset value, beginning of period..........................             $ 10.000
Income from investment operations:
  Net investment income.......................................                 .002
  Net realized and unrealized gain (loss) on investments,
    foreign currency and other assets and liabilities.........               (2.372)
                                                                           --------
Total from investment operations..............................               (2.370)
Less distributions from:
  Net investment income.......................................                   --
  Net realized gain on investments............................                   --
                                                                           --------
Total distributions...........................................                   --
                                                                           --------
Net asset value, end of year..................................             $  7.630
                                                                           ========

Total return (%)..............................................               (23.70)
Ratios to average net assets (%):
  Expenses(c).................................................                 2.25%
  Net investment income(c)....................................                  .04%
Supplemental data:
  Net assets at end of year (000s)............................             $  3,754
  Portfolio turnover rate (%).................................                  226
</TABLE>


- ------------
(a)  For the period May 1, 1998 (Commencement of Operations) to December 31,
     1998.
(b)  Rates are annualized, except total returns for periods less than one year.
(c)  Without the waiver of expenses in 1998, the expense ratio would have been
     6.35% and the net investment loss ratio would have been 4.06%.



                                       10
<PAGE>   14

WILLIAM BLAIR INCOME FUND                                                SUMMARY
- --------------------------------------------------------------------------------

INVESTMENT OBJECTIVE: The William Blair Income Fund seeks to provide investors
with as high a level of current income as is consistent with the preservation of
capital by investing primarily in a diversified portfolio of high-grade,
intermediate-term debt securities.

MAIN INVESTMENT STRATEGIES: The Fund invests primarily in a diversified
portfolio of intermediate-term income-producing securities, including government
securities, U.S. dollar-denominated corporate bonds and notes, collateralized
obligations and money market instruments that are rated in one of the top three
categories. The Fund's investments are subject to certain maturity and duration
restrictions, by which the Fund seeks to approximate the total returns of an
intermediate-term debt index while also providing investors with the additional
security of shorter-term obligations. The Adviser continually considers the
Fund's exposure to interest rate risk because, if interest rates increase, the
Fund's yield may increase and the market value of the Fund's securities will
likely decrease, which would cause the Fund's net asset value and total return
to go down. If interest rates decrease, the Fund's yield may decrease and the
market value of the Fund's securities may increase, which would likely increase
the Fund's net asset value and total return.

MAIN RISKS OF INVESTING: The primary risk of investing in the Fund is interest
rate risk. The yield paid by the Fund will vary with changes in interest rates.
As noted above, changes in interest rates may cause changes in the Fund's yield,
net asset value and total return. Investments with longer maturities, which
typically provide higher yield than securities with shorter maturities, may
subject the Fund to increased price changes resulting from market yield
fluctuations. The Fund is also subject to credit risk. The Fund's net asset
value and total return may be adversely affected by the inability of the issuers
of the Fund's securities to make payment at maturity. Of course, the skill of
the Adviser will play a significant role in the Fund's ability to achieve its
investment objective. The Fund's returns will vary, and you could lose money by
investing in the Fund.


FUND PERFORMANCE HISTORY



ANNUAL TOTAL RETURNS. The bar chart below provides an illustration of how the
Fund's performance has varied in each of the last 10 calendar years. The Fund's
past performance does not necessarily indicate how it will perform in the
future.


<TABLE>
<CAPTION>
YEAR             PERCENT
- ----             -------
<S>              <C>
1991              16.47
1992               7.17
1993               7.82
1994              (0.74)
1995              14.37
1996               3.07
1997               8.03
1998               7.07
</TABLE>


HIGHEST AND LOWEST QUARTERLY RETURNS. During the period shown in the bar chart,
the highest return for a quarter was 5.44% (quarter ended 12/31/91) and the
lowest return for a quarter was -1.30% (quarter ended 12/31/92).



AVERAGE ANNUAL TOTAL RETURNS. The following table compares the Fund's average
annual returns for the periods ended December 31, 1998, to a broad-based
securities market index.




<TABLE>
<CAPTION>
                                          1 YEAR     5 YEARS     LIFE OF FUND**
                                          ------     -------     ---------------
<S>                                       <C>        <C>         <C>
Income Fund                                7.07%      6.22%          7.90%
Lehman Intermediate Gov't/Corp. Index*     8.44%      6.60%          8.19%
</TABLE>


- --------------
*    The Lehman Intermediate Government/Corporate Index represents broad
     intermediate government/corporate bond market performance.
**   The Fund's inception was on September 25, 1990.

YIELD: You may obtain the most current yield information for the Fund by calling
1-800-742-7272.



                                       11
<PAGE>   15



FEES AND EXPENSES: This section describes the fees and expenses that you may pay
if you buy and hold Class R shares of the Fund.



SHAREHOLDER FEES. William Blair Mutual Funds Class R shares are no-load
investments, so you will not pay shareholder fees to buy shares, reinvest
dividends in additional shares or exchange into the R Class shares of another
Fund. However, in order to discourage short-term trading, the Fund may charge a
redemption fee of 1% of the value of the shares sold within 180 days of their
purchase. This redemption fee will be retained by the Fund. The Fund discourages
short-term investments in the Fund because they have a negative impact on
remaining shareholders.




<TABLE>
<S>                                                                <C>
Shares held less than 180 days................................        1%
Shares held 180 days or more..................................     None
</TABLE>


ANNUAL FUND OPERATING EXPENSES are paid out of the Fund's assets and include
fees for portfolio management, maintenance of shareholder accounts, shareholder
servicing, accounting and other services. You do not pay these fees directly
but, as the example shows, these costs are borne indirectly by shareholders.



  ANNUAL FUND OPERATING EXPENSES (expenses that are deducted from Fund assets)


<TABLE>
<S>                                                          <C>
Management Fee...........................................      59%
Distribution (Rule 12b-1) Fee............................    None(1)
Other Expenses...........................................      12%
                                                             ----
         Total Annual Fund Operating Expenses............      71%
</TABLE>



- ------------
(1)  The Fund's Board of Directors has approved a shareholder solicitation
     regarding a proposed .25% distribution fee. The proposal is scheduled to be
     voted upon by shareholder of record on , 1999 at a meeting on November 30,
     1999.



EXAMPLE: This example is intended to help you compare the cost of investing in
Class R shares of the Fund with the cost of investing in other mutual funds. The
example assumes that you invest $ 10,000 in the Fund, redeem all of your shares
at the end of the periods shown, earn a 5% return each year incur the same
operating expenses as shown above.




<TABLE>
<CAPTION>
1 YEAR      3 YEARS     5 YEARS    10 YEARS
- ------      -------     -------    --------
<S>           <C>        <C>         <C>
 $73          $228       $396        $885
</TABLE>


FINANCIAL HIGHLIGHTS: The table below is intended to help you understand the
Fund's financial performance for the past several years. The total return
figures show what an investor in the Fund would have earned (or lost) assuming
reinvestment of all dividends and distributions. This information has been
audited by Ernst & Young LLP, whose report, along with the Fund's financial
statement, is included in the annual report, which is available upon request
(see back cover).


<TABLE>
<CAPTION>
                                                                               YEARS ENDED DECEMBER 31
                                                             -----------------------------------------------------------
                                                               1998         1997         1996         1995         1994
                                                             -------      -------      -------      -------      -------
<S>                                                          <C>          <C>          <C>         <C>           <C>
Net asset value, beginning of year...................        $10.410      $10.270      $10.570     $  9.850      $10.580
Income from investment operations:
  Net investment income...............................          .640         .659         .619         .646         .661
  Net realized and unrealized gain (loss) on
    investments.......................................          .076         .140        (.309)        .732        (.741)
                                                             -------      -------      -------      -------      -------
Total from investment operations.....................           .716         .799         .310        1.378        (.080)
Less distributions from:
  Net investment income...............................          .636         .659         .610         .658         .646
  Net realized gain on investments....................            --           --           --           --         .004
                                                             -------      -------      -------      -------      -------
Total distributions..................................           .636         .659         .610         .658         .650
                                                             -------      -------      -------      -------      -------
Net asset value, end of year.........................        $10.490      $10.410      $10.270      $10.570      $ 9.850
                                                             =======      =======      =======      =======      =======
Total return (%).....................................           7.07         8.03         3.07        14.37         (.74)
Ratios to average net assets (%):
  Expenses............................................           .71          .71          .70          .68          .68
  Net investment income...............................          6.81         6.40         5.97         6.24         6.33
Supplemental data:
  Net assets at end of year (000s)....................     $188,051      $160,055     $150,006     $147,370     $143,790
  Portfolio turnover rate (%).........................           96            83           66           54           63
</TABLE>






                                       12
<PAGE>   16

WILLIAM BLAIR READY RESERVES FUND                                        SUMMARY
- --------------------------------------------------------------------------------

INVESTMENT OBJECTIVE: The William Blair Ready Reserves Fund seeks to obtain the
maximum current income consistent with preservation of capital by investing
exclusively in high-quality money market instruments.

MAIN INVESTMENT STRATEGIES: The Fund invests exclusively in short-term U.S.
dollar-denominated domestic and foreign money market instruments, which include
securities issued by domestic and foreign corporations; the U.S. Government, its
agencies and instrumentalities; U.S. and foreign banks; foreign governments; and
multinational organizations (e.g. the World Bank). The Fund invests exclusively
in securities that are high-quality, which means that they are rated in the top
2 categories. These instruments are considered to be among the safest
investments available because of their short maturities, liquidity and
high-quality ratings. The Fund is designed to be highly liquid and seeks to
maintain a net asset value of $1.00 per share. The Fund is designed for
investors who seek to obtain the maximum current income consistent with the
preservation of capital.

MAIN RISKS OF INVESTING: Although the Fund seeks to preserve the value of your
investment at $1.00 per share, it is possible to lose money by investing in the
Fund. As with any money market fund, there is a low risk that the issuers or
guarantors of securities will default on the payment of principal or interest or
the obligation to repurchase securities from the Fund. An investment in the Fund
is not insured or guaranteed by the Federal Deposit Insurance Corporation or any
other government agency. Of course, the skill of the Adviser will play a
significant role in the Fund's ability to achieve its investment objective.


FUND PERFORMANCE HISTORY



ANNUAL TOTAL RETURNS. The bar chart below provides an illustration of how the
Fund's performance has varied in each of the last 10 calendar years. The Fund's
past performance does not necessarily indicate how it will perform in the
future.



<TABLE>
<CAPTION>
YEAR             PERCENT
- ----             -------
<S>              <C>
1989               8.86
1990               7.81
1991               5.64
1992               3.32
1993               2.64
1994               3.67
1995               5.45
1996               4.81
1997               5.04
1998               4.98
</TABLE>




HIGHEST AND LOWEST QUARTERLY RETURNS. During the period shown in the bar chart,
the highest return for a quarter was 9.02% (quarter ended June 30, 1989) and the
lowest return for a quarter was ____% (quarter ended June 30, 1993).



AVERAGE ANNUAL TOTAL RETURNS. The following table compares the Fund's average
annual total returns for the periods ended December 31, 1998, to a broad-based
securities market index.



<TABLE>
<CAPTION>
                                   1 YEAR     5 YEARS    10 YEARS
                                   ------     -------    --------
<S>                                <C>        <C>        <C>
Ready Reserves Fund                 4.98%       4.77%      5.22%
S&P-rated AAA*                      4.97%       4.75%      5.20%
</TABLE>


- ------------
*    The Standard and Poor's-rated AAA Money Market Funds Index includes money
     market mutual funds rated AAA by Standard and Poor's.


YIELD: You may obtain the most current yield information for the Fund by calling
1-800-742-7272.



                                       13
<PAGE>   17




FEES AND EXPENSES: This section describes the fees and expenses that you may pay
if you buy and hold shares of the Fund.



SHAREHOLDER FEES. Shares of the William Blair Ready Reserves Fund are no-load
investments, so you will not pay any shareholder fees to buy shares, reinvest
dividends in additional shares or exchange into the Class R shares of another
Fund.


ANNUAL FUND OPERATING EXPENSES are paid out of the Fund's assets and include
fees for portfolio management, maintenance of shareholder accounts, shareholder
servicing, accounting and other services. You do not pay these fees directly
but, as the example shows, these costs are borne indirectly by shareholders.


  ANNUAL FUND OPERATING EXPENSES (expenses that are deducted from Fund assets)

<TABLE>
<S>                                                                  <C>
Management Fee.....................................................   59%
Other Expenses.....................................................   10%
                                                                     ---
         Total Annual Fund Operating Expenses......................   69%
</TABLE>


EXAMPLE: This example is intended to help you compare the cost of investing in
the Fund with the cost of investing in other mutual funds. The example assumes
that you invest $10,000 in the Fund, redeem all of your shares at the end of the
periods shown, each has a 5% return each year and incur the same operating
expenses as shown above.




<TABLE>
<CAPTION>
1 YEAR      3 YEARS     5 YEARS    10 YEARS
- ------      -------     -------    --------
<S>          <C>         <C>         <C>
 $71         $221        $385        $861
</TABLE>


FINANCIAL HIGHLIGHTS: The table below is intended to help you understand the
Fund's financial performance for the past several years. The total return
figures show what an investor in the Fund would have earned (or lost) assuming
reinvestment of all dividends and distributions. This information has been
audited by Ernst & Young LLP, whose report, along with the Fund's financial
statement, is included in the annual report, which is available upon request
(see back cover).



<TABLE>
<CAPTION>
                                                                            YEARS ENDED DECEMBER 31
                                                     -------------------------------------------------------------------
                                                         1998          1997         1996          1995          1994
                                                     -----------   -----------   -----------   -----------   -----------
<S>                                                  <C>             <C>             <C>             <C>             <C>
Net asset value, beginning of year ...............   $      1.00   $      1.00   $      1.00   $      1.00   $      1.00
Income from investment operations:
  Net investment income ..........................           .05           .05           .05           .05           .04
  Net realized and unrealized gain (loss) on
    investments ..................................            --            --            --            --          (.01)
                                                     -----------   -----------   -----------   -----------   -----------
Total from investment operations .................           .05           .05           .05           .05           .03
Less distributions from:
 Net investment income ...........................           .05           .05           .05           .05           .04
                                                     -----------   -----------   -----------   -----------   -----------
 Total distributions .............................           .05           .05           .05           .05           .04
                                                     -----------   -----------   -----------   -----------   -----------
Capital contribution .............................            --            --            --            --           .01
                                                     -----------   -----------   -----------   -----------   -----------
Net asset value, end of year .....................   $      1.00   $      1.00   $      1.00   $      1.00   $      1.00
                                                     ===========   ===========   ===========   ===========   ===========

Total return (%) .................................          4.98          5.04          4.81          5.45          3.67(a)
Ratios to average net assets (%):
  Expenses .......................................           .69           .70           .71           .72           .71
  Net investment income ..........................          4.87          4.92          4.78          5.30          3.61
Supplemental data:
  Net assets at end of year (000s) ...............   $ 1,189,051   $   904,569   $   760,808   $   703,993   $   521,277
</TABLE>



- ----------
(a)  The total return includes the effect of the investment adviser's capital
     contribution. Without the investment adviser's capital contribution, the
     total return would have been 3.40%.




                                       14
<PAGE>   18


        INVESTMENT OBJECTIVES, PRINCIPAL INVESTMENT STRATEGIES AND RISKS
- --------------------------------------------------------------------------------


Each Fund is a series of William Blair Mutual Funds, Inc., an open-end
management investment company. William Blair & Company, L.L.C. (the "Adviser")
provides management and investment advisory services to the Funds.

The following section takes a closer look at the investment objectives of each
Fund, its principal investment strategies and certain related investment risks.
Each Fund's secondary strategies or investments are described in the Investment
Glossary at the end of this prospectus. In addition, the Statement of Additional
Information contains more detailed information about certain of these practices,
the potential risks and/or the limitations adopted by each Fund to help manage
such risks.

All investments, including those in mutual funds, have risks. No investment is
suitable for all investors. The Growth Fund, Value Discovery Fund, International
Growth Fund and Emerging Markets Growth Fund are intended for long-term
investors. In addition, the International Growth Fund and Emerging Markets
Growth Fund are intended for investors who can accept the risks entailed in
investing in foreign securities. Of course, there can be no assurance that a
Fund will achieve its objective.



                                       15
<PAGE>   19


GROWTH FUND
- --------------------------------------------------------------------------------

GOAL AND STRATEGY

The Growth Fund seeks long-term appreciation of capital by investing in
well-managed companies in growing industries. The Fund invests primarily in a
diversified portfolio of the common stocks and equity-related securities of
domestic companies.

INVESTMENT PROCESS

The Adviser researches the market for companies that have grown more rapidly
than the gross national product from one business cycle to the next. The Fund
may invest in cyclical industries when the Adviser deems them to be at or near
the bottom of their business cycle and expects a multi-year period of sustained
growth. The Adviser seeks growth opportunities by investing in the following
classes of companies in varying proportions:

         LARGE, high quality, seasoned growth companies that have demonstrated
         sustained growth over a long period of time;

         MEDIUM-sized companies of recognized investment quality whose records
         of sales and earnings growth are not as well established; and

         SMALL, emerging, rapid-growth companies that have had especially
         vigorous growth in revenues and earnings.

The Adviser will invest in companies that it believes are well-managed
considering some or all of the following investment criteria:

         A LEADER IN THE FIELD. The company should be, or clearly have the
         expectation of becoming, a significant provider in the primary markets
         it serves.

         UNIQUE OR SPECIALTY COMPANY. The company should have some distinctive
         attribute that cannot easily be duplicated by present or potential
         competitors. This may take the form of proprietary products or
         processes, a unique distribution system, an entrenched brand name or an
         especially strong financial position.

         QUALITY PRODUCTS OR SERVICES. The company's products or services should
         be regarded as being of superior quality, which should enable the
         company to obtain a premium price and to command greater customer
         loyalty.

         MARKETING CAPABILITY. The company should have a distinctive capability
         in sales, service or distribution.

         VALUE TO CUSTOMER. The prices of the company's products or services
         should be based upon their value to the customer, rather than their
         production cost.

         RETURN ON EQUITY. The company should have achieved, or have the
         potential to achieve, an above-average return on equity through
         efficient use of assets and adequate margins, rather than excessive
         financial leverage. Such companies should be able to finance most or
         all of their growth internally and translate revenue and income growth
         into rising per share earnings and dividends.

         CONSERVATIVE FINANCIAL POLICIES AND ACCOUNTING PRACTICES. The company
         should have a relatively simple, clean financial structure and adhere
         to conservative and straightforward accounting practices.



                                       16
<PAGE>   20


PORTFOLIO SECURITIES

The Fund invests primarily in a diversified portfolio of the common stocks of
domestic companies and related equity securities. To a limited extent, the Fund
may invest in depository receipts, illiquid securities, investment companies,
when-issued and delayed delivery securities and repurchase agreements which are
described in the Investment Glossary at the end of this prospectus. The
Investment Glossary also describes the Fund's policies with regard to borrowing,
concentration, diversification and portfolio turnover. The Fund may invest to a
limited extent in warrants, which are described in the Statement of Additional
Information.

INVESTMENT RISKS

Because the Fund invests substantially all of its assets in common stocks, the
main risk is that the value of the stocks it holds may decrease in response to
the activities of an individual company or in response to general market,
business and economic conditions. If this occurs, the Fund's share price may
also decrease. Stocks of smaller companies involve greater risk than those of
larger, more established companies. This is because smaller companies may be in
earlier stages of development, may be dependent on a small number of products or
services, may lack substantial capital reserves and/or do not have proven track
records. Smaller companies may be more adversely affected by poor economic or
market conditions, and may be traded in low volumes, which may increase
volatility and liquidity risks. The Fund is not intended to be a complete
investment program and there is no assurance that its investment objective can
be achieved.

Generally, the Fund will remain fully invested, and the Adviser will not attempt
to time the market. However, if a significant adverse market action is
anticipated, investment-grade debt securities may be held without limit as a
temporary defensive measure. Normally, the Fund does not purchase any stocks
with a view to quick turnover for capital gains. When the Fund is invested
defensively, it may not achieve its investment objective.

PORTFOLIO MANAGEMENT

The Growth Fund is co-managed by Rocky Barber and Mark A. Fuller, III.

Rocky Barber, a principal of William Blair & Company, L.L.C., has co-managed the
Fund since 1992. He joined William Blair in 1986 as a portfolio manager and
manager of the Investment Management Department. In addition to his management
responsibilities, he is a member of the department's Growth team. Previously, he
was an equity and fixed-income manager with Alliance Capital Management for nine
years and president of the Alliance Capital Bond Fund, a group of fixed-income
mutual funds. Rocky is president of William Blair Mutual Funds, Inc. and a past
Chairman of the Board of Trustees of the Stanford Business School Trust. He
currently serves on the Board of the LaRabida Children's Hospital Foundation and
is a member of the Investment Analysts Society of Chicago. Education:
B.A., M.S. and M.B.A., Stanford University; and CFA.

Mark A. Fuller, III, a principal of William Blair & Company, L.L.C., has
co-managed the Fund since 1992. He has been with William Blair since 1983. He
began his career in Institutional Sales, developing long-standing relationships
with each of the firm's research analysts. He is a portfolio manager for
numerous accounts and is a member of the department's Small Cap and Aggressive
Growth teams. Prior to joining William Blair, he was a sales representative with
IBM Corporation. Education: B.A., Northwestern University; M.B.A., Northwestern
University Kellogg Graduate School of Management.



                                       17
<PAGE>   21


VALUE DISCOVERY FUND
- --------------------------------------------------------------------------------

GOAL AND STRATEGY

The Value Discovery Fund's objective is to seek long-term capital appreciation.
The Fund pursues its objective by investing with a value discipline primarily in
a diversified portfolio of the equity securities of small companies.

INVESTMENT PROCESS

In selecting companies for investment, the Adviser evaluates the extent to which
a company meets the investment criteria set forth below. The weight given to a
particular investment criterion will depend upon the circumstances, and some
Fund holdings may not meet all of the following criteria, which are described
more fully in the Statement of Additional Information:

         MATERIAL PRICE/VALUE DISPARITY--whether the company's current market
         value reflects a material discount from the Adviser's estimate of the
         company's intrinsic value.

         PROBABLE EXPANSION IN PROFITABILITY--whether the company has a
         reasonable expectation of improving its level of profitability over a
         three-year investment horizon.

         SKILLED AND COMMITTED MANAGEMENT--whether the company has a capable and
         skilled management team and a clearly articulated and logical business
         strategy with a reasonable probability of successful execution.

         STRONG CAPITAL STRUCTURE--whether the company has a relatively simple,
         clean financial structure without excessive use of financial leverage.
         In addition, the company should adhere to conservative and
         straightforward accounting practices.

         POSITIVE CATALYST--the likelihood that the company will undergo a
         positive corporate change within a three-year investment horizon.

PORTFOLIO SECURITIES

Generally, most of the Fund's assets will be invested in the common stocks of
small companies. The Fund may also hold debentures and preferred stocks if they
are convertible into common stocks that meet the Fund's investment criteria. The
Fund may invest up to 15% of its net assets in foreign securities, which may
include American Depository Receipts or substantially similar investments;
however, the Fund may invest only up to 5% of its net assets directly in foreign
securities. To a limited extent, the Fund may invest in depository receipts,
foreign securities, illiquid securities, investment companies, real estate
investment trusts, repurchase agreements and when-issued and delayed delivery
securities which are described in the Investment Glossary at the end of this
prospectus. The Investment Glossary also describes the Fund's policies with
regard to borrowing, concentration, diversification and portfolio turnover. The
Fund may invest to a limited extent in warrants and futures, which are described
in the Statement of Additional Information.



                                       18
<PAGE>   22


INVESTMENT RISKS

Because the Fund invests substantially all of its assets in common stocks, the
main risk is that the value of the stocks it holds may decrease in response to
the activities of an individual company or in response to general market,
business and economic conditions. If this occurs, the Fund's share price may
also decrease. Stocks of smaller companies involve greater risk than those of
larger, more established companies. This is because smaller companies may be in
earlier stages of development, may be dependent on a small number of products or
services, may lack substantial capital reserves and/or do not have proven track
records. Smaller companies may be more adversely affected by poor economic or
market conditions, and may be traded in low volumes, which may increase
volatility and liquidity risks. From time to time, the Fund may invest in the
equity securities of very small companies, often referred to as "micro-cap"
companies. The considerations noted above are generally intensified for these
investments. Any convertible debentures issued by small companies are likely to
be lower-rated or non-rated securities, which generally involve more credit risk
than debentures in the higher rating categories and generally include some
speculative characteristics, including uncertainties or exposure to adverse
business, financial or economic conditions which could lead to inadequate
capacity to meet timely interest and principal payments. The Fund is not
intended to be a complete investment program and there is no assurance that its
investment objective can be achieved.

Generally, the Fund will remain fully invested, and the Adviser will not attempt
to time the market. However, if a significant adverse market action is
anticipated, investment-grade debt securities may be held without limit as a
temporary defensive measure. Normally, the Fund does not purchase securities
with a view to quick turnover for capital gains. When the Fund is invested
defensively, it may not achieve its investment objective.

PORTFOLIO MANAGEMENT

The Value Discovery Fund is co-managed by Glen A. Kleczka, David S. Mitchell and
Capucine E. Price.

Glen Kleczka joined William Blair's Investment Management Services in 1996 to
lead the Fund's portfolio management team. For the previous 7 years, he was a
partner in the Private Markets and U.S. Equity groups of Brinson Partners, Inc.
and co-managed the Post-Venture Fund, whose assets totaled more than $900
million. Glen was also a member of the Private Markets Committee which approved
all venture capital and partnership investments. Previously, he spent two years
at CNA Financial Corp. as a manager of their Variable Annuity Trust equity
portfolio. While at the University of Wisconsin he was a participant at the
Center for Applied Security Analysis, a nationally recognized investment
management program. He is a member of the Investment Analyst Society of Chicago.
Education: B.S., Marquette University; M.B.A., University of Wisconsin.

David Mitchell joined William Blair in 1996 as a portfolio manager for the Fund.
In 1996, he was a partner in the U.S. Equity group of Brinson Partners, Inc. and
a member of the Post-Venture Fund management team, whose assets totaled more
than $900 million. Prior to joining Brinson, he spent four years as a co-manager
of Thomas Paine Investors, L.P., a private small-cap fund. Before joining Thomas
Paine, he was a Senior Equity Analyst on NBD's small-cap Woodward Opportunity
Fund and with Connecticut National Bank as an equity analyst and portfolio
manager. Prior to graduate studies he worked as an equity trader and a money
market portfolio manager. Education: B.A., Knox College; M.M., Northwestern
University.


Capucine "Cappy" Price joined William Blair in 1996 as a portfolio manager for
the Fund. For the previous 3 years, she was a partner in the Private Markets and
U.S. Equity groups of Brinson Partners, Inc. and a member of the Post-Venture
Fund management team, whose assets totaled more than $900 million. Previously,
she was an equity analyst for the First National Bank of Chicago. While
attending Northwestern University she was a participant in First Chicago's First
Scholar program. Education: B.A., University of Michigan; M.A., University of
Chicago; M.M., Northwestern University.




                                       19
<PAGE>   23

INTERNATIONAL GROWTH FUND
- --------------------------------------------------------------------------------

GOAL AND STRATEGY

The International Growth Fund seeks long-term capital appreciation through
investment in well-managed, quality growth companies. Current income is not an
investment objective, although it is anticipated that capital appreciation will
normally be accompanied by modest investment income, which may vary depending on
the allocation of the investments.

INVESTMENT PROCESS

Stock Selection. In selecting companies for investment, fundamental company
analysis and stock selection are the Adviser's primary investment criteria. The
Adviser seeks companies that historically have had superior growth,
profitability and quality relative to local markets and relative to companies
within the same industry worldwide, and that are expected to continue such
performance. Such companies generally will exhibit superior business
fundamentals, including leadership in their field, quality products or services,
distinctive marketing and distribution, pricing flexibility and revenue from
products or services consumed on a steady, recurring basis. These business
characteristics should be accompanied by management that is shareholder
return-oriented and uses conservative accounting policies. Companies with
above-average returns on equity, strong balance sheets and consistent,
above-average earnings growth at reasonable valuation levels will be the primary
focus. Stock selection will take into account both local and global comparisons.


Country Allocation. In pursuing the Fund's investment objective, the Adviser
will vary the geographic diversification and types of securities based upon the
Adviser's continuous evaluation of economic, market and political trends
throughout the world. The investment of the Fund's assets in various
international securities markets tends to decrease the degree to which events in
any one country can affect the entire Fund. In making decisions regarding the
country allocation, the Adviser will consider such factors as the conditions and
growth potential of various economies and securities markets, currency exchange
rates, technological developments in the various countries and other pertinent
financial, social, national and political factors. Normally, the Fund's
investments will be spread throughout the world (excluding the United States).
The Adviser intends to maintain approximately 10 to 20 percent of the Fund's
assets in emerging markets, although that allocation will vary over time.
Emerging market companies are (i) companies organized under the laws of an
emerging market country or having securities which are traded principally on an
exchange or over-the-counter in an emerging market country; or (ii) companies
which, regardless of where organized or traded, have a significant amount of
assets (at least 50%) located in and/or derive a significant amount of their
revenues (at least 50%) from goods purchased or sold, investments made or
services performed in or with emerging market countries. Currently, emerging
markets include every country in the world other than the United States, Canada,
Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European
countries. The Adviser will seek investment opportunities in companies at
different stages of development ranging from large, well-established companies
to smaller companies at an earlier stage of development.


PORTFOLIO SECURITIES

The Fund's assets normally will be allocated among not fewer than six different
countries and will not concentrate investments in any particular industry.
However, the Fund may have more than 25% of its assets invested in any major
industrial or developed country. No more than 50% of the Fund's equity
securities may be invested in securities of issuers of any one country at any
given time.

The Fund ordinarily will invest at least 80% of its total assets in a
diversified portfolio of common stocks with above-average growth, profitability
and quality characteristics, issued by companies domiciled outside the U.S., and
in securities convertible into, exchangeable for or having the right to buy such
common stocks. For liquidity purposes, up to 20% of the Fund's assets may be
held in cash (U.S. dollars and foreign currencies) or in short-term securities,
such as repurchase agreements, and domestic and foreign money market
instruments, such as government obligations, certificates of deposit, bankers'
acceptances, time deposits, commercial paper and short-term corporate debt
securities. The Fund does not have specific rating requirements for its
short-term securities; however, the



                                       20
<PAGE>   24


Adviser presently does not intend to invest more than 5% of the Fund's net
assets in securities rated lower than investment grade.


The Fund may enter into forward foreign currency transactions in an effort to
protect against changes in foreign exchange rates. To a limited extent, the Fund
may also invest in depository receipts, foreign currency futures, forward
foreign currency transactions, illiquid securities, investment companies,
repurchase agreements and when-issued and delayed-delivery securities, which are
described in the Investment Glossary at the end of this prospectus. The
Investment Glossary also describes the Fund's policies with regard to borrowing,
concentration, diversification, and portfolio turnover. The Fund may invest to a
very limited extent in warrants, which are described in the Statement of
Additional Information.


INVESTMENT RISKS

General. Because the Fund invests substantially all of its assets in common
stocks, the main risk is that the value of the stocks it holds may decrease in
response to the activities of an individual company or in response to general
market, business and economic conditions. If this occurs, the Fund's share price
may also decrease.

Country Allocation. The Fund seeks to invest in companies and governments of
countries having stable or improving political environments; however, there is
the possibility of expropriation or confiscatory taxation, seizure or
nationalization of foreign bank deposits or other assets, establishment of
exchange controls, the adoption of foreign government restrictions and other
adverse political, social or diplomatic developments that could affect
investments in these nations.

The risks of investing in securities of foreign issuers may include less
publicly available information, less governmental regulation and supervision of
foreign stock exchanges, brokers and issuers, a lack of uniform accounting,
auditing and financial reporting standards, practices and requirements, the
possibility of expropriation, nationalization, confiscatory taxation, adverse
changes in investment or exchange control regulations, political instability,
restrictions on the flow of international capital and difficulty in obtaining
and enforcing judgments against foreign entities. Securities of some foreign
issuers are less liquid and their prices more volatile than the securities of
U.S. companies. In addition, the time period for settlement of transactions in
foreign securities generally is longer than for domestic securities.

The securities held by the Fund will usually be denominated in currencies other
than the U.S. dollar. Therefore, changes in foreign exchange rates will affect
the value of the securities held in these Funds either beneficially or
adversely. Fluctuations in foreign currency exchange rates will also affect the
dollar value of dividends and interest earned, gains and losses realized on the
sale of securities and net investment income and gains, if any, available for
distribution to shareholders.


Operating Expenses. The Fund is expected to incur operating expenses that are
higher than those of mutual funds investing exclusively in U.S. equity
securities, since expenses such as custodial fees related to foreign investments
are usually higher than those associated with investments in U.S. securities.
Similarly, brokerage commissions on purchases and sales of foreign securities
are generally higher than on domestic securities. In addition, dividends and
interest from foreign securities may be subject to foreign withholding taxes
(see "Your Account -- Taxes").



Temporary Defensive Position. Although the Fund will normally invest at least
80% of its assets in the equity securities of companies domiciled outside of the
U.S., the Fund may significantly alter its make-up as a temporary defensive
strategy. A defensive strategy would only be employed if, in the judgment of the
Adviser, investments in international equity securities became decidedly
unattractive because of current or anticipated adverse economic, financial,
political and social factors. The types of securities that might be acquired and
held for defensive purposes could include fixed-income securities and securities
issued by the U.S. or foreign governments as well as domestic or foreign money
market instruments and non-convertible preferred stock, each of which would be
of investment-grade. At such time as the Adviser determines that the Fund's
defensive strategy is no longer warranted, the Fund will adjust its portfolio
back to its normal complement of international equity securities as soon as
practicable.



Smaller Stocks. Stocks of smaller companies involve greater risk than those of
larger, more established companies. This is because smaller companies may be
dependent on a small number of products or services, may lack




                                       21
<PAGE>   25



substantial capital reserves and/or do not have proven track records. Smaller
companies may be more adversely affected by poor economic or market conditions,
and may be traded in low volumes, which may increase volatility and liquidity
risks. The Fund is not intended to be a complete investment program and there is
no assurance that its investment objective can be achieved.


PORTFOLIO MANAGEMENT

The International Growth Fund is managed by W. George Greig.

W. George Greig, a principal of William Blair & Company, L.L.C., has managed the
Fund since 1996 when he joined the Investment Management Department as an
international portfolio manager. He headed international equities for PNC Bank
in Philadelphia from 1995 to 1996 and, prior to that, he was a founding partner
of Pilgrim Baxter & Associates, where he was an analyst, research director and
portfolio manager for over ten years. He also served as chief investment officer
of Framlington Group plc during its association with Pilgrim Baxter and founded
and managed a joint venture between the two firms. Education: B.S.,
Massachusetts Institute of Technology; M.B.A., Wharton School of the University
of Pennsylvania.



                                       22
<PAGE>   26


EMERGING MARKETS GROWTH FUND
- --------------------------------------------------------------------------------
GOAL AND STRATEGY

The investment objective of the Emerging Markets Growth Fund is long-term
capital appreciation. The Fund pursues its objective by investing in a
diversified portfolio of equity securities issued by companies in emerging
economies worldwide.

INVESTMENT PROCESS

The Adviser seeks well-managed, high quality growth companies. Such companies
will generally exhibit superior business fundamentals, including one or more of
the following characteristics:

         REGIONAL LEADERSHIP in product quality or cost competitiveness;

         DOMINANT OR IMPROVING MARKET POSITION, generally associated with a
         competitive advantage in distribution, pricing or business franchise,
         within a growing local or regional economy; and

         SUSTAINABLE ABOVE-AVERAGE AND/OR INCREASING RETURNS on invested capital
         generated from the efficient utilization of assets, increasing profit
         margins or sound financial management, including improvements that may
         arise from the process of privatization or restructuring of corporate
         assets.

The research approach used in stock selection will focus intensively on the
soundness of corporate management, taking into account management's orientation
toward outside shareholders, incentives and ability to execute successful
strategies, commitment to transparent and conservative financial reporting
policies, and general integrity. Current income is not an investment objective,
although it is anticipated that capital appreciation will normally be
accompanied by modest investment income, which may vary depending upon the
allocation of the investments.

In pursuing the Fund's investment objective, the Adviser will vary the Fund's
geographic diversification and types of securities based upon the Adviser's
continuous evaluation of economic, market and political trends throughout the
world. The investment of the Fund's assets in various international securities
markets tends to decrease the degree to which events in any one country can
affect the entire Fund. In making decisions regarding the country allocation,
the Adviser will consider such factors as the conditions and growth potential of
various economies and securities markets, currency exchange rates, technological
developments in the various countries and other pertinent financial, social,
national and political factors. In addition, the Adviser will seek investment
opportunities in companies at different stages of development ranging from
large, well-established companies to smaller companies at an earlier stage of
development.

PORTFOLIO SECURITIES

The Fund pursues its objective by investing primarily in equity securities
issued by emerging market companies. Emerging market companies are (i) companies
organized under the laws of an emerging market country or having securities
which are traded principally on an exchange or over-the-counter in an emerging
market country; or (ii) companies which, regardless of where organized or
traded, have a significant amount of assets (at least 50%) located in and/or
derive a significant amount of their revenues (at least 50%) from goods
purchased or sold, investments made or services performed in or with emerging
market countries. Currently, emerging markets include every country in the world
other than the United States, Canada, Japan, Australia, New Zealand, Hong Kong,
Singapore and most Western European countries.

The Fund normally will allocate its investments among not less than six
different countries and will not concentrate investments in any particular
industry. No more than 50% of the Fund's equity securities will be invested in
securities of issuers in one country at any given time.

The Fund ordinarily will invest at least 65% of its total assets in equity
securities issued by emerging market companies. Equity securities include
securities convertible into, exchangeable for or having the right to buy common
stocks. For liquidity purposes, up to 35% of the Fund's assets may be held in
cash (U.S. dollars and



                                       23
<PAGE>   27



foreign currencies) or in short-term securities, such as repurchase agreements,
and domestic and foreign money market instruments, such as government
obligations, certificates of deposit, bankers' acceptances, time deposits,
commercial paper and short-term corporate debt securities. The Fund does not
have specific rating requirements for its short-term securities; however, the
Adviser presently does not intend to invest more than 5% of the Fund's net
assets in securities rated below investment grade.


The Fund may enter into forward foreign currency transactions in an effort to
protect against changes in foreign exchange rates. To a limited extent, the Fund
may also invest in depository receipts, foreign currency futures, illiquid
securities, investment companies, repurchase agreements and when-issued and
delayed delivery securities which are described in the Investment Glossary at
the end of this prospectus. The Investment Glossary also describes the Fund's
policies with regard to borrowing, concentration, diversification and portfolio
turnover. The Fund intends to invest to a very limited extent in warrants, which
are described in the Statement of Additional Information.

INVESTMENT RISKS


General. Because the Fund invests substantially all of its assets in common
stocks, the main risk is that the value of the stocks it holds may decrease in
response to the activities of an individual company or in response to general
market, business and economic conditions. If this occurs, the Fund's share price
may also decrease.



Country Allocation. The Fund seeks to invest in companies and governments of
countries having stable or improving political environments; however, there is
the possibility of expropriation or confiscatory taxation, seizure or
nationalization of foreign bank deposits or other assets, establishment of
exchange controls, the adoption of foreign government restrictions and other
adverse political, social or diplomatic developments that could affect
investments in these nations.


The risks of investing in securities of foreign issuers may include less
publicly available information, less governmental regulation and supervision of
foreign stock exchanges, brokers and issuers, a lack of uniform accounting,
auditing and financial reporting standards, practices and requirements, the
possibility of expropriation, nationalization, confiscatory taxation, adverse
changes in investment or exchange control regulations, political instability,
restrictions on the flow of international capital and difficulty in obtaining
and enforcing judgments against foreign entities. Securities of some foreign
issuers are less liquid and their prices more volatile than the securities of
U.S. companies. In addition, the time period for settlement of transactions in
foreign securities generally is longer than for domestic securities.

These risks are typically intensified in emerging markets, which are the less
developed and developing nations. Certain of these countries have in the past
failed to recognize private property rights and have at times nationalized and
expropriated the assets of private companies.


Emerging Markets. Investments in emerging markets companies are speculative and
subject to special risks. Political and economic structures in many of these
countries may be in their infancy and developing rapidly. Such countries may
also lack the social, political and economic characteristics of more developed
countries. The currencies of certain emerging market countries have experienced
a steady devaluation relative to the U.S. dollar, and continued devaluations may
adversely affect the value of a fund's assets denominated in such currencies.
Many emerging market countries have experienced substantial rates of inflation
for many years, and continued inflation may adversely affect the economies and
securities markets of such countries.


In addition, unanticipated political or social developments may affect the
values of the Fund's investments in emerging market countries and the
availability to the Fund of additional investments in these countries. The small
size, limited trading volume and relative inexperience of the securities markets
in these countries may make the Fund's investments in such countries illiquid
and more volatile than investments in more developed countries, and the Fund may
be required to establish special custodial or other arrangements before making
investments in these countries. There may be little financial or accounting
information available with respect to issuers located in these countries, and it
may be difficult as a result to assess the value or prospects of an investment
in such issuers.



                                       24
<PAGE>   28



In many foreign countries there is less government supervision and regulation of
business and industry practices, stock exchanges, brokers and listed companies
than in the U.S. There is an increased risk, therefore, of uninsured loss due to
lost, stolen, or counterfeit stock certificates. Prior governmental approval of
non-domestic investments may be required under certain circumstances in some
developing countries, and the extent of foreign investment in domestic companies
may be subject to limitation in other developing countries. Foreign ownership
limitations also may be imposed by the charters of individual companies in
developing countries to prevent, among other concerns, violation of foreign
investment limitations. Repatriation of investment income, capital and proceeds
of sales by foreign investors may require governmental registration and/or
approval in some developing countries. The Fund could be adversely affected by
delays in or a refusal to grant any required governmental registration or
approval for such repatriation.


Further, the economies of certain developing countries may be dependent upon
international trade and, accordingly, have been and may continue to be adversely
affected by trade barriers, exchange controls, managed adjustments in relative
currency values and other protectionist measures imposed or negotiated by the
countries with which they trade. These economies also have been and may continue
to be adversely affected by economic conditions in the countries with which they
trade.

The securities held by the Fund will usually be denominated in currencies other
than the U.S. dollar. Therefore, changes in foreign exchange rates will affect
the value of the securities held in the Fund either beneficially or adversely.
Fluctuations in foreign currency exchange rates will also affect the dollar
value of dividends and interest earned, gains and losses realized on the sale of
securities and net investment income and gains, if any, available for
distribution to shareholders.

The Fund may invest in Russian securities. Russian securities involve additional
significant risks, including political and social uncertainty (for example,
regional conflicts and risk of war), currency exchange rate volatility,
pervasiveness of corruption and crime in the Russian economic, social and legal
systems, delays in settling Fund transactions and risk of loss arising out of
Russia's system of share registration and custody. Russia's system of share
registration and custody creates certain risks of loss (including the risk of
total loss) that are not normally associated with investments in other
securities markets.


Smaller Stocks. Stocks of smaller companies involve greater risk than those of
larger, more established companies. This is because smaller companies may be in
earlier stages of development, may be dependent on a small number of products or
services, may lack substantial capital reserves and/or do not have proven track
records. Smaller companies may be more adversely affected by poor economic or
market conditions, and may be traded in low volumes, which may increase
volatility and liquidity risks. From time to time, the Fund may invest in the
equity securities of very small companies, often referred to as "micro-cap"
companies. The considerations noted above are generally intensified for these
investments. Any convertible debentures issued by small companies are likely to
be lower-rated or non-rated securities, which generally involve more credit risk
than debentures in the higher rating categories and generally include some
speculative characteristics, including uncertainties or exposure to adverse
business, financial or economic conditions which could lead to inadequate
capacity to meet timely interest and principal payments.



Operating Expenses. The Fund is expected to incur operating expenses that are
higher than those of mutual funds investing exclusively in U.S. equity
securities, since expenses such as custodial fees related to foreign investments
are usually higher than those associated with investments in U.S. securities.
Similarly, brokerage commissions on purchases and sales of foreign securities
are generally higher than on domestic securities. In addition, dividends and
interest from foreign securities may be subject to foreign withholding taxes.
(For more information, see "Your Account --Taxes.")



Temporary Defensive Position. Although the Fund will normally invest at least
65% of its assets in the equity securities of emerging market companies, the
Fund may significantly alter its make-up as a temporary defensive strategy. A
defensive strategy would be employed only if, in the judgment of the Adviser,
investments in emerging market equity securities became decidedly unattractive
because of current or anticipated adverse economic, financial, political and
social factors. The types of securities that might be acquired and held for
defensive purposes could include fixed-income securities and securities issued
by the U.S. or foreign governments as well as domestic or foreign money market
instruments and non-convertible preferred stock, each of which would be of





                                       25
<PAGE>   29



investment-grade. At such time as the Adviser determines that the Fund's
defensive strategy is no longer warranted, the Fund will adjust its Fund back to
its normal complement of emerging market equity securities as soon as
practicable. When the Fund is invested defensively, it may not meet its
investment objective. The Fund is not intended to be a complete investment
program, and there is no assurance that its investment objective can be
achieved.


PORTFOLIO MANAGEMENT

The Emerging Markets Growth Fund is co-managed by W. George Greig and Jeffrey A.
Urbina.

W. George Greig, a principal of William Blair & Company, L.L.C., has co-managed
the Fund since its inception in 1998. He joined the Investment Management
Department in 1996 as an international portfolio manager. He headed
international equities for PNC Bank in Philadelphia from 1995 to 1996 and, prior
to that, he was a founding partner of Pilgrim Baxter & Associates, where he was
an analyst, research director and portfolio manager for over ten years. He also
served as chief investment officer of Framlington Group plc during its
association with Pilgrim Baxter and founded and managed a joint venture between
the two firms. Education: B.S., Massachusetts Institute of Technology; M.B.A.,
Wharton School of the University of Pennsylvania.

Jeffrey A. Urbina joined William Blair & Company, L.L.C. in 1996 and has
co-managed the Fund since its inception in 1998. In addition to the Emerging
Market Growth Fund, he is responsible for emerging market research for the
William Blair International Growth Fund. From 1991 to 1996, Mr. Urbina was
Senior Vice President/Director of Emerging Market Research and a Portfolio
Manager for the Van Kampen American Capital Navigator Fund, an emerging market
equity fund listed in Luxembourg. During his five years at Van Kampen American
Capital, he also served as Director of Fixed Income Research and was a member of
the Investment Policy Committee. Before joining Van Kampen American Capital, Mr.
Urbina spent ten years at Citicorp in various capacities, including as a Vice
President in the commercial real estate group in Chicago and as a commercial
lending officer in the bank's Denver office. Mr. Urbina began his banking career
at Harris Bank in Chicago, where he was an International Banking Officer.
Education: B.A., Northwestern University; M.B.A., Northwestern University
Kellogg Graduate School of Management.



                                       26
<PAGE>   30


INCOME FUND
- --------------------------------------------------------------------------------
GOAL AND STRATEGY

The Income Fund pursues its investment objective of providing investors with as
high a level of current income as is consistent with preservation of capital by
investing primarily in a diversified portfolio of high-grade intermediate-term
debt securities.

INVESTMENT PROCESS

The Adviser seeks to outperform the total return of an index of broad
intermediate-term government and corporate high-grade debt through an actively
managed diversified portfolio of debt securities. The Adviser's investment
philosophy emphasizes shifts in the Fund's portfolio among various sectors of
the debt market, subject to the Fund's credit quality constraints for its
portfolio. The Adviser also actively manages the Fund based upon the average
duration and yield to maturity of the Fund's portfolio and the Adviser's
perceived trends in interest rates.

PORTFOLIO SECURITIES

As a matter of fundamental policy, under normal conditions at least 90% of the
Fund's assets will be invested in the following:

          U.S. DOLLAR-DENOMINATED CORPORATE DEBT SECURITIES (domestic or
          foreign) with long-term ratings of "A-" or better, or an equivalent
          rating, by at least one of the following four nationally recognized
          statistical rating organizations ("Rating Organizations"): Duff &
          Phelps, Inc., Fitch Investors Service, Inc., Moody's Investors
          Service, Inc. and Standard & Poor's Corporation;

          OBLIGATIONS OF OR GUARANTEED BY THE UNITED STATES GOVERNMENT, its
          agencies or instrumentalities. These securities include direct
          obligations of the U.S. Treasury, which differ only in their interest
          rates, maturities and time of issuance and obligations issued or
          guaranteed by U.S. Government agencies or instrumentalities, which
          differ in the degree of support provided by the U.S. Government.
          Although these securities are subject to the market risks resulting
          from fluctuation in interest rates, they will be paid in full if held
          to maturity;

          COLLATERALIZED OBLIGATIONS, which are debt securities issued by a
          corporation, trust or custodian, or by a U.S. Government agency or
          instrumentality, that are collateralized by a portfolio or pool of
          assets, such as mortgages, mortgage-backed securities, debit balances
          on credit card accounts or U.S. Government securities. The issuer's
          obligation to make interest and/or principal payments is secured by
          the underlying pool or portfolio of securities. The Income Fund may
          invest in collateralized obligations that are not guaranteed by a U.S.
          Government agency or instrumentality only if the collateralized
          obligations are rated A- or better, or an equivalent rating, by one of
          the Rating Organizations; and

          COMMERCIAL PAPER obligations rated within the highest grade by one of
          the four Rating Organizations.

Up to 10% of the Fund's total assets may be invested in unrated debt securities,
provided that the Adviser deems such securities to be of at least "A-" quality
and provided that the comparable debt of the issuer has a rating of at least
"A-" or its equivalent by one of the four Rating Organizations.

The anticipated dollar-weighted average maturity of the Fund is three to seven
years. The anticipated weighted average modified duration for the Fund is two to
five years, with a maximum duration on any instrument of eight years. The
Adviser will not continue to hold a security whose duration has moved above
eight years.

The duration of an instrument is different from the maturity of an instrument in
that duration measures the average period remaining until the discounted value
of the amounts due (principal and interest) under the instrument are to be paid,
rather than by the instrument's stated final maturity. For example, a portfolio
duration of five years means that if interest rates increased by one percent,
the value of the portfolio would decrease by approximately five percent.
Modified duration adjusts duration to take into account the yield to maturity
and the number of coupons



                                       27
<PAGE>   31



received each year. For purposes of calculating duration, instruments allowing
prepayment will be assigned a maturity schedule by the Adviser based upon
industry experience.


Generally the Fund will remain fully invested. However, the Fund for temporary
defensive purposes may invest up to 100% of its assets in other types of
securities, including high-quality commercial paper, obligations of banks and
savings institutions, U.S. Government securities, government agency securities
and repurchase agreements, or it may retain funds in cash. The Fund does not
invest in equity securities.

To a limited extent, the Fund may invest in illiquid securities, repurchase
agreements and when-issued and delayed delivery securities, which are described
in the Investment Glossary at the end of this prospectus. The Investment
Glossary also describes the Fund's policies with regard to borrowing,
concentration, diversification and portfolio turnover. In addition, the Fund's
policy regarding lending portfolio securities is described in the Statement of
Additional Information.

INVESTMENT RISKS

The Income Fund's investments are subject to price fluctuations resulting from
various factors, including rising or declining interest rates (interest rate
risk). The value of the portfolio's investments (other than an interest-only
class of a collateralized obligation) tends to decrease when interest rates rise
and tends to increase when interest rates fall. In addition, investments with
longer maturities, which typically provide better yields, may subject the Fund
to increased price changes resulting from market yield fluctuations.

The value of the Fund's securities is subject to the ability of the issuers of
such securities to make payment at maturity (credit risk). However, in the
opinion of the Adviser, the risk of loss of principal should be reduced due to
the relatively high quality of the investments in which the Fund primarily will
invest. Obligations that are unrated are not necessarily of lower quality than
those that are rated, but may be less marketable and, consequently, provide
higher yields. Not all securities issued or guaranteed by agencies or
instrumentalities of the U.S. Government are backed by the full faith and credit
of the United States. Such securities involve different degrees of government
backing. Some obligations issued or guaranteed by U.S. Government agencies or
instrumentalities in which the Fund may invest are backed by the full faith and
credit of the United States, such as modified pass-through certificates issued
by the Government National Mortgage Association, while others are backed
exclusively by the agency or instrumentality with limited rights of the issuer
to borrow from the U.S. Treasury (such as obligations of the Federal National
Mortgage Association and the Federal Home Loan Mortgage Corporation). Others are
backed only by the credit of the issuer itself (such as obligations of the
Student Loan Marketing Association). For a description of ratings, see Appendix
B in the Statement of Additional Information.

PORTFOLIO MANAGEMENT

The Income Fund is co-managed by Bentley Myer and James Kaplan.

Bentley Myer, a principal of William Blair & Company, L.L.C., has managed the
Fund since 1992. He joined the firm in 1991 as a fixed-income portfolio manager.
From 1983 to 1991, he was associated with LaSalle National Trust, first as head
of fixed-income investments and later as chief investment officer. Prior to
that, Bentley was head of the municipal investment section of the trust
department of Harris Trust and Savings Bank. He is currently a Trustee of Delnor
Community Hospital, as well as a member of the Investment Analysts Society of
Chicago. Education: B.A., Middlebury College; M.B.A., Wharton School of the
University of Pennsylvania.

Jim Kaplan, an associate of William Blair & Company, L.L.C., has co-managed the
Fund since 1999. He joined the firm's Investment Management Services department
in 1994 as a fixed-income portfolio manager. Prior to that, he was with First
Union National Bank for twelve years. While at First Union, Jim completed their
management training program in lending. His other responsibilities included
trading fixed-income securities such as money markets, municipal bonds and
mortgage backed securities. Jim also assisted in the management of the bank's
portfolio. Education:  B.A., Washington & Lee University.



                                       28
<PAGE>   32


READY RESERVES FUND
- -------------------------------------------------------------------------------
GOAL AND STRATEGY

The Ready Reserves Fund pursues its investment objective of obtaining the
maximum current income consistent with preservation of capital by investing
exclusively in high-quality money market instruments. These instruments are
considered to be among the safest investments available because of their short
maturities, liquidity and high-quality ratings. The Fund seeks to maintain a net
asset value of $1.00 per share. Nevertheless, there is no guarantee that the
objective of the Fund will be achieved or that the net asset value of $1.00 per
share of the Fund will be maintained.

PORTFOLIO SECURITIES

The Fund will invest exclusively in U.S. dollar-denominated money market
instruments, including, but not limited to, those issued by:

          --   Corporations;
          --   The U.S. Government, its agencies and instrumentalities;
          --   U.S. and foreign banks;
          --   Municipalities;
          --   Foreign governments; and
          --   Multinational organizations, such as the World Bank.


The Fund has adopted certain investment policies designed to limit the market
and financial risks of the Fund. The Fund complies with the requirements of Rule
2a-7 under the Investment Company Act of 1940, which governs the maturity and
credit quality of money market funds. The Fund may only invest in securities
that, based on their short-term ratings, are deemed to be the highest grade, or
if unrated, are of equivalent quality in the judgment of the Adviser, subject to
the supervision of the Board of Directors. However, the Fund may invest up to 5%
of its total assets in securities deemed within the second highest grade, or if
unrated, are of equivalent quality. In addition, portfolio investments will be
limited to instruments that the Adviser, under the supervision of the Board of
Directors, has determined present minimal credit risks. Securities are deemed to
be highest grade if they are rated high-quality by two Rating Organizations, or,
if only rated by one Rating Organization, rated high-quality by that Rating
Organization. For example, commercial paper rated "Duff 1 minus," "Fitch 1,"
"Prime 1" and "A-1" by Duff & Phelps, Inc., Fitch Investors Service, Inc.,
Moody's Investors Service, Inc., and Standard & Poor's Corporation,
respectively, would be considered high quality. Obligations that are unrated are
not necessarily of lower quality than those that are rated, but may be less
marketable and, consequently, may provide higher yields. Further, the Fund may
invest in other corporate obligations maturing in thirteen months or less, such
as publicly traded bonds, debentures and notes, if they are rated within the two
highest grades by a Rating Organization. For a description of these ratings, see
Appendix B to the Statement of Additional Information.



To a limited extent, the Fund may invest in repurchase agreements, Section 4(2)
commercial paper, when-issued and delayed delivery securities and variable rate
securities, which are more fully described in the Investment Glossary at the end
of this prospectus. The Investment Glossary also describes the Fund's policies
with regard to borrowing, concentration and diversification.


INVESTMENT RISK

The yield paid by the Ready Reserves Fund will vary with changes in interest
rates. While the Fund seeks to maintain its $1.00 share price, there is no
guarantee that it will be able to do so.



                                       29
<PAGE>   33


PORTFOLIO MANAGEMENT


The Ready Reserves Fund is co-managed by Bentley Myer and James Kaplan.


Bentley Myer, a principal with William Blair & Company, L.L.C., has managed the
Fund since 1992. He joined the firm in 1991 as a fixed-income portfolio manager.
From 1983 to 1991 he was associated with LaSalle National Trust, first as head
of fixed-income investments and later as chief investment officer. Prior to
that, Bentley was head of the municipal investment section of the trust
department of Harris Trust and Savings Bank. He is currently a Trustee of Delnor
Community Hospital as well as a member of the Investment Analysts Society of
Chicago. Education: B.A., Middlebury College; M.B.A., Wharton School of the
University of Pennsylvania.


Jim Kaplan, an associate of William Blair & Company, L.L.C., has co-managed the
Fund since 1999. He joined the firm's Investment Management Services department
in 1994 as a fixed-income portfolio manager. Prior to that, he was with First
Union National Bank for twelve years. While at First Union, Jim completed their
management training program in lending. His other responsibilities included
trading fixed-income securities such as money markets, municipal bonds and
mortgage backed securities. Jim also assisted in the management of the bank's
portfolio.  Education:  B.A., Washington & Lee University.




                                       30
<PAGE>   34



                             MANAGEMENT OF THE FUNDS
- --------------------------------------------------------------------------------
DIRECTORS, OFFICERS AND ADVISER. The Board of Directors of William Blair Mutual
Funds, Inc. has overall management responsibility. The duties of the directors
and officers of the Fund include supervising the business affairs of the Fund,
monitoring investment activities and practices and considering and acting upon
future plans for the Fund. The Statement of Additional Information has the names
of and additional information about the directors and officers of the Fund. The
Adviser, William Blair & Company, L.L.C., 222 West Adams Street, Chicago,
Illinois 60606, is responsible for providing investment advisory and management
services to the Funds of the Fund, subject to the direction of the Board of
Directors. The Adviser is also the principal underwriter and distributor of the
Fund and acts as agent of the Fund in the sale of its shares (the
"Distributor"). William Blair & Company, L.L.C. was founded over 60 years ago by
William McCormick Blair. Today, the firm has 150 principals and 600 employees.
The main office in Chicago houses all research and investment management
services.



The Investment Management Department oversees the assets of William Blair mutual
funds, along with corporate pension plans, endowments and foundations and
individual accounts. The department currently manages approximately $12 billion
in equities, fixed-income securities and cash equivalents.


The Adviser firmly believes that clients are best served when portfolio managers
are encouraged to draw on their experience and develop new ideas. This
philosophy has helped build a hard-working, results-oriented team of over 30
portfolio managers, supported by over 40 analysts, with an exceptionally low
turnover rate. William Blair portfolio managers generally average more than ten
years with William Blair and more than two decades of experience in the
investment industry. The Adviser is registered as an investment adviser under
the Investment Advisers Act of 1940.

Each Fund pays the Adviser a monthly investment management fee. Fees paid for
each Fund's most recently completed fiscal year are shown below:


<TABLE>
<CAPTION>
                                            FEE AS A % OF
FUND                                      AVERAGE NET ASSETS
- ----                                      ------------------
<S>                                       <C>
Growth Fund                                     0.75%
Value Discovery Fund                            1.15%
International Growth Fund                       1.10%
Emerging Markets Growth Fund                    1.40%
Income Fund                                     0.59%
Ready Reserves Fund                             0.59%
</TABLE>

CUSTODIAN. The Custodian is Investors Bank and Trust Company, 200 Clarendon
Street, Boston, Massachusetts 02117. State Street Bank and Trust Company, 225
Franklin Street, Boston, Massachusetts 02110, may serve as the Custodian for
Individual Retirement Accounts ("IRAs").

TRANSFER AGENT AND DIVIDEND PAYING AGENT. The Transfer Agent and Dividend Paying
Agent is State Street Bank and Trust Company, 225 Franklin Street, Boston,
Massachusetts 02110.


YEAR 2000. A critical issue has emerged in the investment services industry and
for the economy overall regarding how existing application software programs and
operating systems can accommodate the date value for the year 2000. Many
existing application software products in the marketplace were designed only to
accommodate a two-digit date position which represents the year (e.g., "95" is
stored on the system and represents the year 1995). As a result, the year 1999
(i.e., "99") could be the maximum date value these systems will be able to
accurately process. The Fund is in the process of working with the Adviser and
other service providers to assure that the Fund is prepared for the year 2000.
The Fund has been assured by the Adviser and other service providers that they
do not believe that the Fund will be materially adversely affected by year 2000.
Nevertheless, the inability of the Adviser and other service providers to
successfully address year 2000 issues could result in interruptions in the
Fund's business and have a material adverse effect on the Fund's operations.
Year 2000 problems would also increase the risks of the Fund's investments. To
assess the potential effect of the year 2000 problem, the Adviser is reviewing
information regarding the year 2000 readiness of issuers of securities the Fund
may purchase. However, this may




                                       31
<PAGE>   35



be difficult with certain issuers. For example, a Fund that deals with foreign
service providers or invests in foreign securities will have difficulty
determining the year 2000 readiness of those entities. This is especially true
of entities or issuers in emerging markets. The financial impact of these issues
for the Fund is still being determined. There can be no assurance that potential
year 2000 problems would not have a material adverse effect on the Fund.

PENDING CHANGES TO THE FUND. The Board of Directors of the Fund has approved a
proxy solicitation of shareholders of record as of __________, 1999. The matters
to be considered by all shareholders include the election of Board members,
ratification of auditors, and approval of a change in or elimination of certain
fundamental investment restrictions, including certain investment objectives. In
addition, the Class R shareholders will be asked to approve a Distribution Plan
under Rule 12b-1 of the Investment Company Act of 1940. The shareholder meeting
is scheduled to be held on November 30, 1999.




                                       32
<PAGE>   36



                                  YOUR ACCOUNT
- --------------------------------------------------------------------------------
R CLASS SHARES



The R Class shares offered herein for the Growth Fund, Value Discovery Fund,
International Growth Fund, Emerging Markets Growth Fund and Income Fund are
offered only to investors who acquire the shares directly through the Fund's
distributor or through a select number of financial intermediaries with whom the
distributor has entered into selling agreements specifically authorizing them to
sell R Class shares.


HOW TO BUY SHARES (By Mail, by Wire or by Telephone)


MINIMUM INVESTMENTS. To open an account, the minimum initial investment for
regular accounts is $5,000, and the minimum initial investment for Individual
Retirement Accounts ("IRAs") is $2,000. To add to an account, the minimum
subsequent investment is generally $1,000 for all accounts, except accounts
holding shares of the Ready Reserves Fund, for which the subsequent minimum
investment is $1. The Funds may accept smaller amounts under a group payroll
deduction or similar plan. These minimum amounts may be changed at any time and
may be waived for directors, principals, officers or employees of the Funds or
the Adviser.



PURCHASE PRICE. All Funds Class R Shares are sold at their public offering
price, which is the net asset value per share that is next computed after
receipt of your order in proper form by the Distributor, the Transfer Agent or a
designated agent thereof. For the Ready Reserves Fund, shares are sold at the
net asset value per share that is next computed after receipt of your order in
proper form by the Distribution, the Transfer Agent or a designated agent
thereof. The net asset value per share of the Ready Reserves Fund normally will
be $1.00. (For more information, see "Determination of Net Asset Value.") If you
fail to pay for your order, you will be liable for any loss to the Funds and, if
you are a current shareholder, the Funds may redeem some or all of your shares
to cover such loss.


NOTE: All purchases made by check should be in U.S. dollars and made payable to
William Blair Mutual Funds, Inc., or in the case of a retirement account, the
custodian or trustee of such account. Third party checks will not be accepted.
When purchases are made by check or periodic account investment, the Funds may
delay sending redemption proceeds until they determine that collected funds have
been received for the purchase of such shares, which may be up to 15 calendar
days.


RIGHT TO REJECT YOUR PURCHASE ORDER. The Fund reserves the right to decline your
purchase order upon receipt for any reason, including excessive, short-term
(market-timing) or other abusive trading practices which may disrupt portfolio
management strategies and harm Fund performance. To minimize harm to the Funds
and their shareholders, the each Fund reserves the right to reject any purchase
order (including exchanges) from any investor it believes has a history of
abusive trading or whose trading, in its judgment, has been or may be disruptive
to a Fund. In making this judgment, the Funds may consider trading done in
multiple accounts under common ownership or control. The Funds also reserve the
right to delay delivery of redemption proceeds -- up to seven days -- or to
honor certain redemptions with securities, rather than cash.


BY MAIL

OPENING AN ACCOUNT. To open a new account by mail (except for the Ready Reserves
Fund), make out a check for the amount of your investment, payable to "William
Blair Mutual Funds, Inc." Complete the account application included with this
Prospectus and mail the completed application and the check to the Transfer
Agent, State Street Bank and Trust Company ("State Street"), P.O. Box 9104,
Boston, Massachusetts 02266-9104.

For the Ready Reserves Fund, send your check and completed application to the
Distributor, William Blair Mutual Funds, Inc., 222 West Adams Street, Chicago,
Illinois 60606.

ADDING TO AN ACCOUNT. To purchase additional shares, make out a check for the
amount of your investment, payable to "William Blair Mutual Funds, Inc." Except
for the Ready Reserves Fund, mail the check, together with a letter that
specifies the portfolio name, the account number and the name(s) in which the
account is registered, to State Street Bank and Trust Company, P.O. Box 9104,
Boston, Massachusetts 02266-9104.



                                       33
<PAGE>   37


For the Ready Reserves Fund, send your check and letter to the Distributor,
William Blair Mutual Funds, Inc. 222 West Adams Street, Chicago, Illinois 60606.

BY WIRE

OPENING AN ACCOUNT. First, call State Street at 1-800-635-2886 (in
Massachusetts, 1-800-635-2840) for an account number. Then instruct your bank to
wire federal funds to:

         State Street Bank and Trust Co.
         ABA # 011000028
         DDA # 99029340
         Attn:  Custody & Shareholder Services
         225 Franklin Street
         Boston, Massachusetts 02110

Include the portfolio name in which you are investing, your assigned account
number and the name(s) in which the account is registered. Finally, complete the
account application, indicate the account number assigned to you by State Street
and mail it to William Blair Mutual Funds, Inc., 222 West Adams Street, Chicago,
Illinois 60606.

ADDING TO AN ACCOUNT. To add to your account by wire, instruct your bank to wire
federal funds to:

         State Street Bank and Trust Co.
         ABA # 011000028
         DDA # 99029340
         Attn:  Custody & Shareholder Services
         225 Franklin Street
         Boston, Massachusetts 02110

In your request, specify the portfolio name in which you are investing, your
account number, and the name(s) in which the account is registered.

To add to an existing account by wire transfer of funds, you must have selected
this option on your account application.

BY TELEPHONE

OPENING AN ACCOUNT. See "By Wire."

ADDING TO AN ACCOUNT. Call State Street at 1-800-635-2886 (in Massachusetts,
1-800-635-2840). For the Ready Reserves Fund only, call your William Blair
account executive at (312) 364-8000.

Tell your account executive the portfolio name, your account number and the
name(s) in which the account is registered. You may then pay for your new shares
by mail or by wire.

To add to an existing account by telephone, you must have selected this option
on your account application.

HOW TO SELL SHARES (By Mail, by Wire or by Telephone)

You can arrange to take money out of your account by selling ("redeeming") some
or all of your shares. You may give instructions to redeem your shares by mail,
by wire or by telephone, as described below.

BY MAIL

For all Funds except the Ready Reserves Fund, to redeem shares by mail, send a
written redemption request signed by all account owners to State Street Bank and
Trust Company, P.O. Box 9104, Boston, Massachusetts 02266-9104.



                                       34
<PAGE>   38


For the Ready Reserves Fund, send your redemption request signed by all account
owners to the Distributor, William Blair & Company, L.L.C., 222 West Adams
Street, Chicago, Illinois 60606, to the attention of your account executive.
Amounts redeemed will be placed in your brokerage account.

FOR ALL FUNDS, WRITTEN REDEMPTION REQUESTS MUST INCLUDE:

          --   a letter that contains your name, the Fund's name and the dollar
               amount or number of shares to be redeemed;

          --   any stock certificates endorsed, or accompanied by an endorsed
               stock power, to the order of the Fund; and

          --   any other necessary documents, such as an inheritance tax consent
               or evidence of authority (for example, letters testamentary),
               dated not more than 60 days prior to receipt thereof by State
               Street or the Distributor.

BY WIRE

To redeem some or all of your shares in any Funds by wire, you may contact the
Transfer Agent, or the Distributor in the case of the Ready Reserves Fund, by
mail or telephone, as explained herein. To redeem by wire, you must have elected
this option on your account application and attached to the application a
voided, unsigned check or deposit slip for your bank account.

BY TELEPHONE

TO REDEEM SHARES BY TELEPHONE, YOU MUST HAVE ELECTED THIS OPTION ON YOUR ACCOUNT
APPLICATION. For all Funds except the Ready Reserves Fund, contact the Transfer
Agent at 1-800-635-2886 (in Massachusetts, 1-800-635-2840).

For the Ready Reserves Fund, you may redeem some or all of your shares by
telephone by calling your William Blair account executive at (312) 364-8000.
Amounts redeemed will be placed in your brokerage account.

NOTE: Redemption requests should NOT be sent to the Fund or to the Distributor
(except in the case of the Ready Reserves Fund).

SIGNATURE GUARANTEES. Signature guarantees must be obtained from a bank that is
a member of the FDIC, by a brokerage firm that is a member of the NASD, or by an
eligible guarantor who is a member of, or a participant in, a signature
guarantee program. Your redemption request must include a signature guarantee if
any of the following situations apply:

          --   You wish to redeem shares having a value of $5,000 or more in a
               single transaction;

          --   Your account registration has changed; or

          --   You want a check in the amount of your redemption to be mailed to
               a different address than the one on your account application
               (address of record).

SIGNATURE GUARANTEES, IF REQUIRED, MUST APPEAR ON THE WRITTEN REDEMPTION REQUEST
AND ON ANY ENDORSED STOCK CERTIFICATE OR STOCK POWER.

REDEMPTION PRICE. The redemption price that you receive for your shares may be
more or less than the amount that you originally paid for them, depending upon
their net asset value at the time your redemption request is received in proper
order by the Distributor, the Transfer Agent or a designated agent thereof. For
the Ready Reserves Fund, the net asset value will usually be $1.00.



                                       35
<PAGE>   39


PAYMENT FOR REDEEMED SHARES. Payment normally will be mailed to you at the
address of record for your account by the third business day after receipt by
State Street (or, in the case of the Ready Reserves Fund, the Distributor) of a
redemption request and any other required documentation and after any checks in
payment for your shares have cleared.

For the Ready Reserves Fund, if the Distributor receives notice of your request
to redeem shares by 9:30 a.m., Chicago time, the redemption will be effected as
of that date and proceeds normally will be paid that day. If notice of your
redemption request is received after that time, proceeds normally will not be
paid until the next business day.


ABUSIVE TRADING PRACTICES. Excessive, short-term (market-timing) or other
abusive trading practices may disrupt portfolio management strategies and harm
Fund performance. To minimize harm to the Funds and their shareholders, the
Funds reserve the right to reject any purchase order (including exchanges) from
any investor believed to have a history of abusive trading or whose trading, in
the Funds' judgment, has been or may be disruptive to a Fund. In making this
judgment, the Funds may consider trading done in multiple accounts under common
ownership or control. The Funds also reserve the right to delay delivery of your
redemption proceeds -- up to seven days -- or to honor certain redemptions with
securities, rather than cash, as described in the next section. In addition,
redemption of shares from a Fund, other than the Ready Reserves Fund, within 180
days of purchase may be subject to a 1% redemption fee.


REDEMPTIONS IN KIND. If the Adviser determines that existing conditions make
cash payments undesirable, redemption payments may be made in whole or in part
in securities or other financial assets, valued for this purpose as they are
valued in computing the NAV for each of the Fund's shares. Shareholders
receiving securities or other financial assets on redemption may realize a gain
or loss for tax purposes, and will incur any costs of sale, as well as the
associated inconveniences. Notwithstanding the above, each of the Funds are
obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of
the net asset value of such Fund during any 90-day period for any one
shareholder of record.


AUTOMATIC REDEMPTION OF SMALL ACCOUNTS. Because of the relatively high cost of
maintaining small accounts, the Fund reserves the right to redeem your shares in
any account that, following a redemption, is below a specified amount.
Currently, the MINIMUM IS $5,000 PER ACCOUNT. Before the redemption is
processed, you will be notified that the value of your account has fallen below
the minimum and allowed to make an additional investment.


SPECIAL REDEMPTION METHODS FOR THE READY RESERVES FUND. In addition to the above
methods, shares of the Ready Reserves Fund can be redeemed by two other methods
unique to this Fund. Redemption requests will be processed after the next daily
dividend declaration at the net asset value next determined upon receipt by the
Distributor of a proper redemption request. In this way, you will receive the
net asset value of your shares and all declared but unpaid dividends on your
shares through the date of redemption.

          1. REDEMPTION BY CHECK. To redeem shares by check, you must fill out
          the appropriate section of your account application. If your
          application for the check-writing privilege is approved, you will be
          provided with checks that may be made payable to any person IN AN
          AMOUNT NOT LESS THAN $500 NOR MORE THAN $9 MILLION. There currently is
          no charge for this service and no limit on the number of checks that
          you may write; however, these provisions are subject to change.

          The payee of the check may cash or deposit it like any other check
          drawn on a bank. When the check is presented for payment, a sufficient
          number of full and fractional shares from your account will be
          redeemed at their next-determined net asset value per share, usually
          $1.00, to cover the amount of the check. This enables you to continue
          earning daily dividends until the check clears. Canceled checks will
          be returned to you by State Street. For joint accounts, unless a
          single signer has been authorized on your account application, checks
          must be signed by all joint account owners.

          The Fund may refuse to honor checks whenever the right of redemption
          has been suspended or postponed or whenever your account is otherwise
          impaired. For instance, your account would be considered to be
          impaired when (1) there are insufficient assets to cover the check,
          (2) a "stop order" has been placed on the check, and (3) in other
          situations, such as where there is a dispute over ownership of the
          your account. A



                                       36
<PAGE>   40


          $25 SERVICE FEE may be charged when a check is presented to redeem
          shares in excess of the value of your account or for an amount less
          than $500.

          2. AUTOMATIC REDEMPTION. The Distributor has instituted an automatic
          redemption procedure available to Ready Reserve Fund shareholders who
          maintain certain brokerage accounts with it. The Distributor may use
          this procedure to satisfy amounts due it by you as a result of
          purchases of securities or other transactions in your brokerage
          account. Under this procedure, if you so elect, your brokerage account
          will be scanned at the opening of business each day and, after
          application of any cash balances in the brokerage account, a
          sufficient number of shares will be redeemed, effective that day at
          the next-determined net asset value, to satisfy any amounts which you
          are obligated to pay to the Distributor. You will receive all
          dividends declared but unpaid through the date of redemption.



                                       37
<PAGE>   41



HOW TO EXCHANGE SHARES (By Mail or by Telephone)

- --   Growth Fund

- --   Value Discovery Fund

- --   International Growth Fund

- --   Emerging Markets Growth Fund

- --   Income Fund

- --   Ready Reserves Fund


Subject to the following limitations, you may exchange shares of Class R shares
of each Fund into either Class R shares of another Fund or into shares of the
Ready Reserves Fund at their relative net asset values so long as the shares to
be acquired are available for sale in your state of residence. There is NO
SERVICE FEE for an exchange; however, ONLY FOUR (4) EXCHANGES FROM A FUND ARE
ALLOWED WITHIN ANY 12-MONTH PERIOD. Exchanges will be effected by redeeming your
shares and purchasing shares of the other Fund or Funds requested.


BY MAIL

You may request an exchange of your shares by writing to William Blair Mutual
Funds, Inc., Attention: Exchange Department, P.O. Box 9104, Boston,
Massachusetts 02266-9104.

BY TELEPHONE

You may also exchange your shares by telephone by completing the appropriate
section on your account application. Once your telephone authorization is on
file, State Street will honor your requests to redeem shares by telephone at
1-800-635-2886 (in Massachusetts, 1-800-635-2840). If you hold certificated
shares, you must deposit them with State Street prior to any exchange of such
shares.

Neither the Funds nor State Street will be liable for any loss, expense or cost
arising out of any telephone request pursuant to the telephone exchange
privilege, including any fraudulent or unauthorized request, and you will bear
the risk of loss, so long as the Funds or the Transfer Agent reasonably
believes, based upon reasonable verification procedures, that the telephonic
instructions are genuine. The verification procedures include (1) recording
instructions, (2) requiring certain identifying information before acting upon
instructions and (3) sending written confirmations.

DIVIDENDS AND DISTRIBUTIONS

INCOME DIVIDENDS. Each Fund earns dividends from stocks and interest from bond,
money market, and other investments, which are passed along to shareholders as
income dividends as long as expenses do not exceed income.

CAPITAL GAIN DISTRIBUTIONS. Each Fund realizes capital gains whenever it sells
securities for a higher price than it paid for them, which are passed along to
shareholders as capital gain distributions.

As a shareholder, you are entitled to your portion of the Fund's net income and
gains on its investments. Each Fund passes its earnings along to you as
distributions. The Funds' policy is to distribute substantially all net
investment income, if any, and all net realized capital gain, if any. All
distributions of income and capital gain and any return of capital have the
effect of immediately thereafter decreasing net asset value per share. Income
dividends and capital gain distributions will be automatically reinvested in
additional shares at net asset value on the reinvestment date, unless you
specifically request otherwise (see "Shareholder Services and Account Policies
- -- Dividend Options"). Cash payments are made by the Dividend Paying Agent,
State Street Bank and Trust Company, shortly following the reinvestment date.


WHEN DIVIDENDS ARE PAID



     --   For the Growth Fund, Value Discovery Fund, International Growth Fund
          and Emerging Markets Growth Fund, all income dividends, if any, and
          capital gain distributions, if any, generally will be paid in December
          and/or January.




                                       38
<PAGE>   42



     --   For the Income Fund, income dividends are normally paid the fifteenth
          day of each month, if a business day, with net-realized long-term
          capital gain distributions, if any, generally paid in December and/or
          January. The Income Fund attempts to maintain relatively level monthly
          dividends and, from time to time, may distribute or retain net
          investment income and capital gain or make a return of capital
          distribution in order to pursue that goal.


     --   For the Ready Reserves Fund, the Fund's net investment income will be
          declared at the close of the New York Stock Exchange on each day that
          the Fund is open for business, which is generally 3:00 p.m., Chicago
          time, as a dividend to shareholders who were of record prior to the
          declaration.


The Funds may vary these dividend practices at any time. Income dividends and
any capital gain distributions on all Funds will vary from year to year.
Dividends and distributions may be subject to withholding, as required by the
Internal Revenue Service (see "Your Account -- Taxes").


TAXES

As with any investment, you should consider how your investment in a Fund will
be taxed. If your account is not a tax-deferred retirement account, you should
be aware of these tax implications.

TAXES ON DISTRIBUTIONS. The Fund's distributions are subject to Federal income
tax and may also be subject to state or local taxes. Distributions may be
taxable at different rates depending upon the length of time the Fund holds the
security. Your distributions are taxable when they are paid, whether you take
them in cash or reinvest them in additional shares. However, dividends declared
in October, November or December to shareholders of record as of a date in one
of those months and paid before the following February 1 are treated as having
been paid on December 31 of the calendar year declared for Federal income tax
purposes. The Funds will inform you of the amount and nature of distributions
paid.

Under the Federal tax laws, income dividends and short-term capital gains
distributions are taxed as ordinary income. Long-term capital gain distributions
are taxed as long-term capital gains. It is anticipated that a portion of the
ordinary income dividends for the Growth Fund and the Value Discovery Fund will
be eligible for the dividends-received deduction available for corporate
shareholders. The ordinary income dividends of International Growth Fund,
Emerging Markets Growth Fund, Income Fund and Ready Reserves Fund are not
eligible for the dividends-received deduction available to corporate
shareholders.

TAXES ON TRANSACTIONS. Redemptions of Fund shares and exchanges for shares of
other Funds are treated as sales and are subject to capital gains taxation. A
capital gain or loss is the difference between the price that you paid for your
shares and the price that you receive when you sell (or exchange) them. For the
Ready Reserves Fund, so long as a net asset value of $1.00 is maintained, the
sale or redemption of your shares will not result in a capital gain or loss. Any
loss recognized on the redemption of shares held six months or less will be
treated as a long-term capital loss to the extent you have received any
long-term capital gain dividends on such shares. A shareholder who redeems
shares normally will recognize a capital gain or loss for Federal income tax
purposes. If you realize a loss on the redemption of Fund shares within 30 days
before or after an acquisition of shares of the same Fund, the two transactions
may be subject to the wash sale rules of the Internal Revenue Code, resulting in
a postponement of the recognition of such loss for Federal income tax purposes.

"BUYING A DIVIDEND." If you buy shares before a Fund deducts a distribution from
its net asset value, you will pay the full price for the shares and then receive
a portion of the price back in the form of a taxable distribution. See "Your
Account -- Dividends and Distributions" for payment schedules, and call the
Distributor if you have further questions.

EFFECT OF FOREIGN TAXES. Investment income received from sources within foreign
countries may be subject to foreign income taxes, which generally will reduce a
Fund's distributions. However, the United States has entered into tax treaties
with many foreign countries that entitle certain investors to a reduced rate of
tax or to certain exemptions from tax. Accordingly, the International Growth
Fund and Emerging Markets Growth Fund will operate so as to qualify for such
reduced tax rates or tax exemptions whenever practicable.

For a more detailed discussion of taxes, see the Statement of Additional
Information.



                                       39
<PAGE>   43


                    DETERMINATION OF NET ASSET VALUE ("NAV")
- --------------------------------------------------------------------------------
WHEN AND HOW NET ASSET VALUE IS DETERMINED

The market value of a mutual fund's total assets, minus liabilities, divided by
the number of shares outstanding, is its net asset value. The value of a single
share is called its share value or share price.

The net asset value per share shall be determined as of the close of trading on
the New York Stock Exchange, which is generally 3:00 p.m., Chicago time (4:00
p.m. Eastern time), on each day when the Exchange is open. In addition, the
Ready Reserves Fund does not price its shares on the observance of Columbus Day
and Veterans Day.

When net asset value is computed, quotations of foreign securities in foreign
currencies are converted into the United States dollar equivalents at the
prevailing market rates as computed by Investors Bank & Trust Company, the
custodian. Trading in securities on exchanges and over-the-counter markets in
Europe and the Far East is normally completed at various times prior to 3:00
p.m., Chicago time, the current closing time of the New York Stock Exchange.
Trading on foreign exchanges may not take place on every day that the New York
Stock Exchange is open. Conversely, trading in various foreign markets may take
place on days when the New York Stock Exchange is not open and on other days
when net asset value is not calculated. Consequently, calculation of the net
asset value for the International Growth Fund and the Emerging Markets Growth
Fund may not occur at the same time as determination of the most current market
prices of the securities included in the calculation, and the value of the net
assets held by the International Growth Fund and the Emerging Markets Growth
Fund may be significantly affected on days when shares are not available for
purchase or redemption.

For the purposes of calculating the net asset value of the Ready Reserves Fund,
portfolio securities are valued at their amortized cost, which means their
acquisition cost adjusted for the amortization of a premium or discount.

HOW THE MARKET VALUE OF FUND SECURITIES IS DETERMINED

DOMESTIC EQUITY SECURITIES. The market value of portfolio domestic equity
securities is determined by valuing securities traded on national securities
markets at the last sale price or, in the absence of a recent sale on the date
of determination, at the latest bid price. Securities traded only on the
over-the-counter market are valued at the latest bid price.

FOREIGN EQUITY SECURITIES. The value of a foreign equity security is determined
based upon the last sale price on the foreign exchange or market on which it is
primarily traded and in the currency of that market, as of the close of the
appropriate exchange or, if there have been no sales during that day, at the
latest bid price.


FIXED-INCOME SECURITIES. Fixed-income securities are valued by using market
quotations or independent pricing services that use either prices provided by
market-makers or matrixes that produce estimates of market values obtained from
yield data relating to instruments or securities with similar characteristics.


OTHER SECURITIES AND ASSETS. Other securities, and all other assets, are valued
at a fair value as determined in good faith by, or under the direction of, the
Board of Directors.



                                       40
<PAGE>   44

                    SHAREHOLDER SERVICES AND ACCOUNT POLICIES
- --------------------------------------------------------------------------------
The Funds provide a variety of services to help you manage your account.


AUTOMATIC SWEEP PROGRAM. You can purchase shares of the Ready Reserves Fund
through an automatic sweep program if you establish a brokerage account with the
Distributor, provided that you meet the current minimum brokerage account size
requirements. The automatic sweep program helps you to make convenient,
efficient use of free credit balances in your William Blair brokerage account.


To purchase shares of the Ready Reserves Fund through the automatic sweep
program, you must have a free credit balance in your brokerage account with the
Distributor. Currently, free credit balances are used automatically to purchase
shares. If you have a FREE CREDIT BALANCE OF AT LEAST $1,000, the Distributor
will effect on your behalf an investment in shares on an expedited basis.

     --   If you have a free credit balance resulting from securities
          transactions in your brokerage account at the opening of business of
          the Distributor, it generally will be invested in shares on that same
          day, but in no event later than the next business day.

     --   If you have a free credit balance resulting from a deposit made prior
          to 2:00 p.m., Chicago time, or a receipt of income (by check or wire),
          then it will be invested in shares no later than the next business
          day.

     --   If you have a free credit balance of at least $1 and less than $1,000,
          it will be invested in shares within a maximum of five business days
          from the day when the free credit balance is created.

DIVIDEND OPTIONS. You may choose to have your distributions reinvested in
additional shares automatically or paid in cash by making the appropriate
election on your account application. You may change your election at any time
by providing written notice to State Street.

         1. AUTOMATIC DIVIDEND REINVESTMENT PLAN. The Funds automatically
reinvest all income dividends and capital gain distributions in additional
shares of stock at net asset value on the reinvestment date. (For more
information, see "Dividend and Distribution Policy.")

         2. CASH-DIVIDEND PLAN. You may choose to have all of your income
dividends paid in cash and/or have your capital gain distributions paid in cash.
Any distributions you do not elect to have paid in cash will be reinvested
automatically in additional shares at net asset value.

         3. AUTOMATIC DEPOSIT OF DIVIDENDS. You may elect to have all income
dividends and capital gain distributions automatically deposited in a previously
established bank account.

AUTOMATIC INVESTMENT PLAN. On your account application, you may authorize State
Street to automatically withdraw an amount of money (MINIMUM $250) from your
bank account on the fifth or twentieth day of each month. This amount will be
invested in additional shares. You may change your election at any time by
providing written notice to State Street.

SYSTEMATIC WITHDRAWAL PLAN. You may establish this plan with shares presently
held or through a new investment, which should be at least $5,000. Under this
plan, you specify a dollar amount to be paid monthly, quarterly or annually.
Shares corresponding to the specified dollar amount are automatically redeemed
from your account on the fifth business day preceding the end of the month,
quarter or year. While this plan is in effect, all income dividends and capital
gain distributions on shares in your account will be reinvested at net asset
value in additional shares. There is no charge for withdrawals, but the MINIMUM
WITHDRAWAL IS $250 PER MONTH. Depending upon the size of payments requested, and
fluctuations in the net asset value of the shares redeemed, redemptions under
this plan may reduce or even exhaust your account.

RETIREMENT PLANS. The Funds offer a variety of qualified retirement plans,
including several types of Individual Retirement Accounts ("IRAs") (e.g.
traditional IRAs, Roth IRAs and education IRAs), Simplified Employee



                                       41
<PAGE>   45



Pension Plans ("SEPs") and other qualified retirement plans. Additional
information concerning such plans is available from the Funds.


The minimum initial retirement plan investment is $2,000 and the minimum
subsequent investment is $1,000. State Street serves as custodian for IRAs.
State Street charges a $5 plan establishment fee, an annual $15 custodial fee
and a $10 fee for each lump sum distribution from a plan. These fees may be
waived under certain circumstances.

With regard to retirement plans:

     --   participation is voluntary;
     --   you may terminate or change a plan at any time without penalty or
          charge from the Funds;
     --   the Funds will pay any additional expenses that they incur in
          connection with such plans;
     --   on your account application, you may select a plan or plans in which
          to invest;
     --   additional forms and further information may be obtained by writing or
          calling the Funds;
     --   the Funds reserve the right to change the minimum amounts for initial
          and subsequent investments or to terminate any of the plans;
     --   the Funds reserve the right to waive investment minimums at the
          discretion of the Distributor; and
     --   the Funds require a copy of the trust agreement when shares are to be
          held in trust.

WRITTEN CONFIRMATIONS. Each purchase, exchange or redemption transaction is
confirmed in writing to the address of record by giving details of the purchase
or redemption.

CERTIFICATED SHARES. In the interest of safekeeping and expediting transfers and
redemptions, most shareholders prefer not to receive certificates for their
shares. Rather, the value of the shares is represented by your account balance.
However, you may obtain certificated shares upon your written request. Unless
payment for shares is made by certified or cashier's check, a share certificate
will not be issued until 30 days after your purchase is completed.

USE OF INTERMEDIARIES. If you purchase or redeem shares through an investment
dealer, bank or other institution, that institution may impose charges for its
services. These charges would reduce your yield or return. You may purchase or
redeem shares directly from the Fund or with the Transfer Agent, State Street
Bank, without any such charges.

TRANSFER OF SHARES. Fund shares may be transferred by a written request
addressed to the Fund and delivered to State Street, giving the name and social
security or taxpayer identification number of the transferee and accompanied by
the same signature guarantees and documents as would be required for a
redemption, together with specimen signatures of all transferees.

SUSPENSION OF OFFERING. The Funds reserves the right to withdraw all or any part
of the offering made by this Prospectus, and the Funds or the Distributor may
reject purchase orders. From time to time, the Funds may temporarily suspend the
offering of shares to new investors. During the period of such suspension,
persons who are already shareholders of a Fund may be permitted to continue to
purchase additional shares of the Fund, to have dividends reinvested and to make
redemptions.

CONSULTATION WITH A PROFESSIONAL TAX ADVISER IS RECOMMENDED, both because of the
complexity of Federal tax laws and because various tax penalties are imposed for
excess contributions to, and late or premature distributions from, IRAs or other
qualified retirement plans. Termination of a plan shortly after its adoption may
have adverse tax consequences.

SHAREHOLDER RIGHTS. All shares of each Fund have equal rights with respect to
dividends, assets and liquidation of a Fund and equal, noncumulative voting
rights. Noncumulative voting rights allow the holder or holders of a majority of
shares, voting together for the election of directors, to elect all the
directors. All shares of each Fund will be voted in the aggregate, except when a
separate vote by Fund is required under the Investment Company Act of 1940 (the
"1940 Act"). Shares are fully paid and nonassessable when issued, are
transferable without restriction, and have no preemptive or conversion rights.
Under Maryland law, the Funds are not required to hold shareholder meetings on
an annual basis. As required by law, the Funds will, however, hold shareholder
meetings when a



                                       42
<PAGE>   46


sufficient number of shareholders request a meeting, or as deemed desirable by
the Board of Directors, for such purposes as electing or removing directors,
changing fundamental policies or approving an investment management agreement.
(For additional information about shareholder voting rights, see the Statement
of Additional Information.)



                                       43
<PAGE>   47


                               INVESTMENT GLOSSARY
- --------------------------------------------------------------------------------
The following glossary explains some of the types of securities in which the
Funds may invest, investment techniques they may employ, and some of the related
risks. For more information, please see the Statement of Additional Information.

BORROWING. To a certain extent, each Fund may borrow money from banks for
limited purposes. The Growth Fund, Value Discovery Fund, International Growth
Fund and Emerging Markets Growth Fund may borrow up to 10% of their total
assets; the Income Fund and Ready Reserves Fund may borrow up to 5% of their
total assets. Most borrowing is intended only as a temporary measure for
extraordinary or emergency purposes, such as to help meet redemption requests,
and not for leverage purposes.

COLLATERALIZED OBLIGATIONS. The Income Fund may invest in collateralized
obligations (debt securities issued by a corporation, trust or custodian or by a
U.S. Government agency or instrumentality), that are collateralized by a
portfolio or pool of assets, such as mortgages, mortgage-backed securities,
debit balances on credit card accounts or U.S. Government securities. The
issuer's obligation to make interest and/or principal payments is secured by the
underlying pool or portfolio of securities.

A variety of types of collateralized obligations are available currently, and
others may become available in the future. Some obligations are for the
guaranteed payment of only principal (the principal-only or "PO" class) or only
interest (the interest-only or "IO" class), while others are for the guaranteed
payment of both, or some variation thereof. The yields to maturity on PO and IO
class obligations are more sensitive than other obligations, with the IO class
obligations being extremely sensitive to the rate of principal payments
(including prepayments) on the related underlying assets. The Fund will invest
only in PO and IO class mortgage obligations collateralized by securities
guaranteed by the U.S. Government. Some types of collateralized obligations may
be less liquid than other types of securities. Investments in collateralized
obligations that are deemed to be illiquid, which includes PO and IO class
mortgage obligations, will be subject to the 15% limitation on illiquid assets.

The mortgage-backed collateralized obligations in which the Fund may invest
include pools of mortgage loans assembled for sale to investors by various
governmental agencies, such as the Government National Mortgage Association
("GNMA") and government-related organizations such as the Federal National
Mortgage Association ("FNMA") and the Federal Home Loan Mortgage Corporation
("FHLMC"). Payments of principal and/or interest on such mortgages, including
prepayments, are guaranteed by the agency or instrumentality. The agencies and
instrumentalities are subject to varying degrees of support by the U.S.
Government. The effective credit quality of collateralized obligations is the
credit quality of the collateral. The requirements as to collateralization are
determined by the issuer or sponsor of the collateralized obligation in order to
satisfy rating agencies. These collateralized obligations generally have excess
collateral, but typically, any guarantee is limited to a specified percentage of
the pool of assets.

The potential for appreciation in the event of a decline in interest rates may
be limited or negated by increased principal prepayments by certain
mortgage-backed securities, such as GNMA Certificates and other collateralized
obligations. During periods of declining interest rates, mortgages underlying
the security are prone to prepayment, causing the security's effective maturity
to be shortened. Prepayment of high interest rate mortgage-backed securities
during times of declining interest rates will tend to lower the return of the
Fund and may even result in losses to the Fund if the prepaid securities were
acquired at a premium. Because mortgage-backed securities tend to be sensitive
to prepayment rates on the underlying collateral, their value to the Fund is
dependent upon the accuracy of the prepayment projections used, which are a
consensus derived from several major securities dealers. The duration of many
mortgage-backed securities changes substantially in response to changes in
interest rates and prepayment rates.

CONCENTRATION. Each of the Funds intends to invest not more than 25% of its
total asset in any one industry; however, the Ready Reserves Fund may invest
more than 25% of its total assets in the domestic banking industry. These
limitations do not apply to U.S. Government securities or government agency
securities, or to instruments, such as repurchase agreements, secured by these
instruments.



                                       44
<PAGE>   48


DEPOSITORY RECEIPTS. The Growth Fund, Value Discovery Fund, International Growth
Fund and Emerging Markets Growth Fund may invest in foreign issuers through
sponsored American Depository Receipts ("ADRs"), European Depository Receipts
("EDRs") and Global Depository Receipts ("GDRs"). Generally, an ADR is a
dollar-denominated security issued by a U.S. bank or trust company that
represents, and may be converted into, the underlying foreign security. An EDR
represents a similar securities arrangement but is issued by a European bank and
a GDR is issued by a depository. ADRs, EDRs and GDRs may be denominated in a
currency different from the underlying securities into which they may be
converted. Typically, ADRs, in registered form, are designed for issuance in
U.S. securities markets, and EDRs and GDRs, in bearer form, are designed for
issuance in European securities markets. Investments in depository receipts
entail risks similar to direct investments in foreign securities. These risks
are detailed in the sections on "Investment Risks" under the "International
Growth Fund" and "Emerging Markets Growth Fund" above and in the Statement of
Additional Information.

DIVERSIFICATION. As a matter of fundamental policy, each Fund will not purchase
the securities of any issuer if, as a result, more than 5% of its total assets
would be invested in such issuer. For the Value Discovery Fund and Emerging
Markets Growth Fund, that limitation applies to 75% of the Fund's net assets. In
addition, each Fund will not purchase more than 10% of the outstanding voting
securities of any issuer. These limitations do not apply to U.S. Government
securities or to government agency or instrumentality securities.

FOREIGN CURRENCY FUTURES. The International Growth Fund and Emerging Markets
Growth Fund may purchase and sell futures on foreign currencies as a hedge
against possible variation in foreign exchange rates. Foreign currency futures
contracts are traded on boards of trade and futures exchanges. A futures
contract on a foreign currency is an agreement between two parties to buy and
sell a specified amount of a particular currency for a particular price on a
future date. To the extent that the Fund engages in foreign currency futures
transactions, but fails to consummate its obligations under the contract, the
net effect to the Fund would be the same as speculating in the underlying
futures contract. Futures contracts entail certain risks. If the Adviser's
judgment about the general direction of rates or markets is wrong, the Fund's
overall performance may be less than if no such contracts had been entered into.
There may also be an imperfect correlation between movements in prices of
futures contracts and the portfolio securities being hedged. In addition, the
market prices of futures contracts may be affected by certain factors. If
participants in the futures market elect to close out their contracts through
offsetting transactions rather than to meet margin requirements, distortions in
the normal relationship between the securities and futures markets could result.
In addition, because margin requirements in the future markets are less onerous
than margin requirements in the cash market, increased participation by
speculators in the futures market could cause temporary price distortions. Due
to price distortions in the futures market and an imperfect correlation between
movements in the prices of securities and movements in the prices of futures
contracts, a correct forecast of market trends by the Fund's Adviser may still
not result in a successful hedging transaction. The Fund could also experience
losses if it could not close out its futures position because of an illiquid
secondary market, and losses on futures contracts are not limited to the amount
invested in the contract. The above circumstances could cause the Fund to lose
money on the financial futures contracts and also on the value of its portfolio
securities.

To the extent required to comply with the Investment Company Act of 1940 (the
"1940 Act") and the rules and interpretations thereunder, whenever the Fund
enters into a futures contract, the Fund will maintain a segregated account
consisting of either cash or liquid securities equal to the Fund's potential
obligation under such contracts. The segregation of assets places a practical
limit on the extent to which the Fund may engage in futures contracts.

To the extent required to comply with CFTC Rule 4.5 and in order to avoid
"commodity pool operator" status, each Fund will not enter into a financial
futures contract if immediately thereafter the aggregate initial margin and
premiums for such contracts held by the Fund would exceed 5% of the liquidation
value of the Fund's assets. The Fund will not engage in transactions in
financial futures contracts for speculation, but only in an attempt to hedge
against changes in interest rates or market conditions affecting the value of
securities that the Fund holds or intends to purchase.

FORWARD FOREIGN CURRENCY TRANSACTIONS. The International Growth Fund and
Emerging Markets Growth Fund may enter into forward foreign currency contracts
as a means of managing the risks associated with changes in exchange rates. A
forward foreign currency contract is an agreement to exchange U.S. dollars for
foreign currencies at a specified future date and specified amount which is set
by the parties at the time of entering into the contract. The Adviser will
generally use such currency contracts to fix a definite price for securities
they have



                                       45
<PAGE>   49


agreed to buy or sell and may also use such contracts to hedge the Fund's
investments against adverse exchange rate changes. Alternatively, the Funds may
enter into a forward contract to sell a different foreign currency for a fixed
U.S. dollar amount where the Adviser believes that the U.S. dollar value of the
currency to be sold pursuant to the forward contract will fall whenever there is
a decline in the U.S. dollar value of the currency in which securities of the
Fund are denominated ("cross-hedge"). The profitability of forward foreign
currency transactions depends upon correctly predicting future changes in
exchange rates between the U.S. dollar and foreign currencies. As a result, a
Fund may incur either a gain or loss on such transactions. While forward foreign
currency transactions may help reduce losses on securities denominated in a
foreign currency, they may also reduce gains on such securities depending on the
actual changes in the currency's exchange value relative to that of the
offsetting currency involved in the transaction. The Funds will not enter into
forward foreign currency transactions for speculative purposes.

ILLIQUID SECURITIES. The Growth Fund, Value Discovery Fund, International Growth
Fund, Emerging Markets Growth Fund and Income Fund may each invest up to 15% of
their net assets in illiquid securities. The Ready Reserves Fund may invest up
to 10% of its net assets in illiquid securities. Illiquid securities are those
securities that are not readily marketable, including restricted securities and
repurchase obligations maturing in more than seven days.

INVESTMENT COMPANIES. Subject to the provisions of the 1940 Act, the Growth
Fund, Value Discovery Fund, International Growth Fund and Emerging Markets
Growth Fund may each invest in the shares of investment companies. Investment in
other investment companies may provide advantages of diversification and
increased liquidity; however, there may be duplicative expenses, such as
advisory fees or custodial fees. Several foreign governments permit investments
by non-residents in their markets only through participation in certain
investment companies specifically organized to participate in such markets. In
addition, investments in unit trusts and country funds permit investments in
foreign markets that are smaller than those in which the Fund would ordinarily
invest directly. Investments in such pooled vehicles should enhance the
geographical diversification of the Fund's assets, while reducing the risks
associated with investing in certain smaller foreign markets. Investments in
such vehicles will provide increased liquidity and lower transaction costs than
are normally associated with direct investments in such markets; however, there
may be duplicative expenses, such as advisory fees or custodial fees.

PORTFOLIO TURNOVER RATE. None of the Funds intend to trade portfolio securities
for the purpose of realizing short-term profits. However, each will adjust its
portfolio as considered advisable in view of prevailing or anticipated market
conditions and the Fund's investment objective, and there is no limitation on
the length of time securities must be held by the Fund prior to being sold. Fund
turnover rate will not be a limiting factor for a Fund. Although each Fund's
turnover rate will vary from year to year, it is anticipated that each Fund's
turnover rate, under normal circumstances, will be less than 100%. A higher
portfolio turnover rate would involve correspondingly higher transaction costs,
which would be borne directly by each Fund.


REAL ESTATE INVESTMENT TRUSTS. The Value Discovery Fund may invest without limit
in real estate investment trusts ("REITs"). REITs are subject to volatility from
risks associated with investments in real estate and investments dependent on
income from real estate, such as fluctuating demand for real estate and
sensitivity to adverse economic conditions. In addition, the failure of a REIT
to continue to qualify as a REIT for tax purposes would have an adverse effect
upon the value of an investment in that REIT.


REPURCHASE AGREEMENTS. Each Fund may invest in repurchase agreements. Repurchase
agreements are instruments under which a Fund acquires ownership of a security,
and the seller, a broker-dealer or a bank agrees to repurchase the security at a
mutually agreed upon time and price. The repurchase agreement serves to fix the
yield of the security during the Fund's holding period. The Funds currently
intend to enter into repurchase agreements only with member banks of the Federal
Reserve System or with primary dealers in U.S. Government securities. In all
cases, the Adviser, subject to the supervision of the Board of Directors, must
be satisfied with the creditworthiness of the seller before entering into a
repurchase agreement. In the event of the bankruptcy or other default of the
seller of a repurchase agreement, the Fund could incur expenses and delays
enforcing its rights under the agreement, and experience a decline in the value
of the underlying securities and loss of income. The maturity of a security
subject to repurchase may exceed one year, and, for the Income Fund, the
modified duration of a security subject to repurchase may exceed eight years.
Repurchase agreements maturing in more than seven days, together with any
securities that are restricted as to disposition under the federal securities
laws or are otherwise considered to be illiquid, will not exceed 15% of the net
assets of the Growth Fund, Value Discovery Fund,



                                       46
<PAGE>   50


International Growth Fund, Emerging Markets Growth Fund and Income Fund and 10%
of the net assets of the Ready Reserves Fund.

SECTION 4(2) PAPER. The Ready Reserves Fund may invest in commercial paper
issued in reliance upon the so-called "private placement" exemption from
registration afforded by Section 4(2) of the Securities Exchange Act of 1933
("Section 4(2) paper"). Section 4(2) paper is restricted as to disposition under
the Federal securities laws, and generally is sold to institutional investors
such as the Fund. Any resale by the purchaser must be in an exempt transaction.
Section 4(2) paper normally is resold to other institutional investors through
or with the assistance of the issuer or investment dealers who make a market in
the Section 4(2) paper, thus providing liquidity. The Adviser considers the
legally restricted but readily saleable Section 4(2) paper to be liquid;
however, pursuant to the procedures approved by the Fund's Board of Directors,
if a particular investment in Section 4(2) paper is not determined to be liquid,
that investment will be included within the limitation on illiquid securities.
The Adviser monitors the liquidity of each investment in Section 4(2) paper on a
continuing basis.

WHEN-ISSUED AND DELAYED DELIVERY SECURITIES. From time to time, in the ordinary
course of business, each Fund may purchase newly issued securities appropriate
for the Fund on a "when-issued" basis, and may purchase or sell securities
appropriate for the Fund on a "delayed delivery" basis. When-issued or delayed
delivery transactions involve a commitment by the Fund to purchase or sell
particular securities, with payment and delivery to take place at a future date.
These transactions allow the Fund to lock in an attractive purchase price or
yield on a security the Fund intends to purchase. Normally, settlement occurs
within one month of the purchase or sale. During the period between purchase and
settlement, no payment is made or received by the Fund and, for delayed delivery
purchases, no interest accrues to the Fund. Because the Fund is required to set
aside cash or liquid securities at least equal in value to its commitments to
purchase when-issued or delayed delivery securities, the Adviser's ability to
manage the Fund's assets may be affected by such commitments. The Fund will only
make commitments to purchase securities on a when-issued or delayed delivery
basis with the intention of actually acquiring the securities, but it reserves
the right to sell them before the settlement date if it is deemed advisable.

VARIABLE RATE SECURITIES. The Ready Reserves Fund may invest in instruments
having rates of interest that are adjusted periodically or that "float"
continuously or periodically according to formulae intended to minimize
fluctuation in values of the instruments ("Variable Rate Securities"). The
interest rate on a Variable Rate Security is ordinarily determined by reference
to, or is a percentage of, an objective standard such as a bank's prime rate,
the 90-day U.S. Treasury Bill rate or the rate of return on commercial paper or
bank certificates of deposit. Generally, the changes in the interest rates on
Variable Rate Securities reduce the fluctuation in the market value of such
securities. Accordingly, as interest rates decrease or increase, the potential
for capital appreciation or depreciation is less than for fixed-rate
obligations. Further, the Fund may invest in Variable Rate Securities that have
a demand feature entitling the Fund to resell the securities to the issuer or a
third party at an amount approximately equal to the principal amount thereof
plus accrued interest ("Variable Rate Demand Securities"). As is the case for
other Variable Rate Securities, the interest rate on Variable Rate Demand
Securities varies according to some objective standard intended to minimize
fluctuation in the values of the instruments. Many of these Variable Rate Demand
Securities are unrated, their transfer is restricted by the issuer, and there is
little if any secondary market for the securities. Thus, any inability of the
issuers of such securities to pay on demand could adversely affect the liquidity
of these securities. The Fund determines the maturity of Variable Rate
Securities in accordance with Securities and Exchange Commission rules, which
allow the Fund to consider certain of such instruments as having maturities
shorter than the maturity date on the face of the instrument if they are
guaranteed by the U.S. Government or its agencies, if they have a stated
maturity date of one year or less, or if they have demand features prior to
maturity.



                                       47
<PAGE>   51


FOR MORE INFORMATION

More information about the Funds is available without charge, upon request,
including the following:

SEMI-ANNUAL/ANNUAL REPORTS

The Semi-Annual and audited Annual Reports to Shareholders include financial
statements, detailed performance information, portfolio holdings and statements
from the Fund managers. In the Fund's Annual Report, you will find a discussion
of the market conditions and investment strategies that the Adviser believes
significantly affected the Fund's performance in its last fiscal year.
Shareholder reports are incorporated by reference into this Prospectus, which
means that they are part of this Prospectus for legal purposes.

STATEMENT OF ADDITIONAL INFORMATION (SAI)

The SAI contains more detailed information about the Funds. The current SAI has
been filed with the Securities and Exchange Commission and is incorporated by
reference into this Prospectus, which means that it is part of this Prospectus
for legal purposes.

TO OBTAIN INFORMATION:

BY TELEPHONE
Call: 1-800-635-2886
(In Massachusetts 1-800-635-2840)

BY MAIL
Write to:
WILLIAM BLAIR MUTUAL FUNDS, INC.
222 West Adams Street
Chicago, Illinois 60606
(312) 364-8000

or

STATE STREET BANK AND TRUST COMPANY
(the Fund's Transfer Agent)
P.O. Box 9104
Boston, MA 02266-9104

ON THE INTERNET

Text-only versions of fund documents can be viewed online or downloaded from the
SEC at http://www.sec.gov

You can also obtain copies by visiting the SEC's Public Reference Room in
Washington, D.C. (1-800-SEC-0330) or by sending your request and a duplicating
fee to the SEC's Public Reference Room Section, Washington, D.C. 20549- 6009.

No person has been authorized to give any information or to make any
representations not contained in this Prospectus and, if given or made, such
information or representations must not be relied upon as having been authorized
by the Funds or their distributor. The Prospectus does not constitute an
offering by the Fund or their distributor in any jurisdiction in which such
offering may not lawfully be made.


William Blair Mutual Funds, Inc.                    May 1, 1999, as supplemented
Investment Company Act File No.: 811-5344           September 30, 1999



<PAGE>   52


The introduction in this Prospectus is not complete and may be changed. We may
not sell these securities until the Registration Statement filed with the
Securities and Exchange Commission is effective. This Prospectus is not an offer
to sell these securities and is not soliciting an offer to buy these securities
in any state where the offer or sale is not permitted.



                             SUBJECT TO COMPLETION


                  PRELIMINARY PROSPECTUS DATED AUGUST 15, 1999



May 1, 1999, as supplemented September 30, 1999



                        WILLIAM BLAIR MUTUAL FUNDS, INC.



                           CLASS A, B, C AND I SHARES



                                  GROWTH FUND


                              VALUE DISCOVERY FUND


                           INTERNATIONAL GROWTH FUND


                          EMERGING MARKETS GROWTH FUND


                                  INCOME FUND


                              READY RESERVES FUND



This prospectus contains important information about each Fund, including their
investment objectives. For your benefit and protection, please read it before
you invest and keep it for future reference. This prospectus relates only to
Class A, Class B, Class C and Class I Shares of each Fund, except for the Ready
Reserves Fund which only has a single class of shares.



THE SECURITIES AND EXCHANGE COMMISSION HAS NOT APPROVED OR DISAPPROVED THESE
SECURITIES OR PASSED UPON THE ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO
THE CONTRARY IS A CRIMINAL OFFENSE.



                        WILLIAM BLAIR MUTUAL FUNDS, INC.


                             222 West Adams Street


                            Chicago, Illinois 60606

<PAGE>   53

TABLE OF CONTENTS


<TABLE>
<S>                                                           <C>
SUMMARY.....................................................    3
         Growth Fund........................................    3
         Value Discovery Fund...............................    5
         International Growth Fund..........................    7
         Emerging Markets Growth Fund.......................   10
         Income Fund........................................   12
         Ready Reserves Fund................................   15
INVESTMENT OBJECTIVES, PRINCIPAL INVESTMENT STRATEGIES AND
  RISKS.....................................................   17
         Growth Fund........................................   18
         Value Discovery Fund...............................   20
         International Growth Fund..........................   22
         Emerging Markets Growth Fund.......................   25
         Income Fund........................................   29
         Ready Reserves Fund................................   31
MANAGEMENT OF THE FUNDS.....................................   33
CHOOSING A SHARE CLASS......................................   35
         Class A Shares.....................................   36
         Class B Shares.....................................   38
         Class C Shares.....................................   40
         Class I Shares.....................................   41
YOUR ACCOUNT................................................   42
         How to Buy Shares..................................   42
         How to Sell Shares.................................   43
         How to Exchange Shares.............................   45
         Dividends and Distributions........................   46
         Taxes..............................................   47
DETERMINATION OF NET ASSET VALUE............................   48
SHAREHOLDER SERVICES AND ACCOUNT POLICIES...................   49
INVESTMENT GLOSSARY.........................................   51
</TABLE>



 2  William Blair Mutual Funds, Inc.  May 1, 1999, as supplemented September 30,
1999

<PAGE>   54

WILLIAM BLAIR GROWTH FUND                                                SUMMARY
- --------------------------------------------------------------------------------
INVESTMENT OBJECTIVE: The William Blair Growth Fund seeks long-term appreciation
of capital by investing in well-managed companies in growing industries.

MAIN INVESTMENT STRATEGIES: The Fund invests primarily in a diversified
portfolio of common stocks of domestic companies. The Adviser seeks growth
opportunities by investing in large, medium and small companies in varying
proportions. With respect to large companies, the Adviser looks for high
quality, seasoned growth companies that have demonstrated sustained growth over
a long period of time. With respect to medium-sized companies, the Adviser
searches for companies that are generally of similar investment quality to large
companies but whose records of sales and earnings growth are not as well
established. With respect to small companies, the Adviser looks for emerging,
rapid growth companies that have had especially vigorous growth in revenues and
earnings. The Fund is designed for long-term investors.

MAIN RISKS OF INVESTING: Since the Fund invests most of its assets in common
stocks, the primary risk is that the value of the stocks it holds might decrease
in response to the activities of an individual company or general economic and
market conditions. If this occurs, the Fund's net asset value may also decrease.
The securities of small and medium size companies may be more volatile and more
speculative than the securities of larger, more established issuers. In
addition, small and medium companies may be traded in low volumes, which can
increase volatility. Of course, the skill of the Adviser will play a significant
role in the Fund's ability to achieve its investment objective. The Fund's
returns will vary, and you could lose money by investing in the Fund.

FUND PERFORMANCE HISTORY


ANNUAL TOTAL RETURNS. The bar chart below provides an illustration of how the
Fund's performance has varied in each of the last 10 calendar years. The Fund's
past performance does not necessarily indicate how it will perform in the
future. The Class A, Class B, Class C and Class I shares are new classes of the
Fund for which performance is not yet available. The Class R shares of the Fund
are offered in a separate prospectus. The returns for the Class A, Class B,
Class C and Class I shares will be substantially similar to those of the Class R
shares shown in the chart below because all shares of the Fund are invested in
the same portfolio of securities. The annual returns of the different Classes of
shares will differ only to the extent that the expenses of the Classes differ.



Class A, B and C share sale loads are not reflected in the chart below. If sales
loads were reflected, the Fund's returns would be less than those shown. Class I
has no sales loads.

[FUND PERFORMANCE HISTORY CHART]


HIGHEST AND LOWEST QUARTERLY RETURNS. During the period shown in the bar chart,
the highest return for a quarter was 23.69% (fourth quarter 1998) and the lowest
return for a quarter was -14.91% (third quarter 1990). Shareholders should be
aware that the Fund is a long-term investment and is not managed for short-term
results.



May 1, 1999, as supplemented September 30, 1999                   Prospectus   3

<PAGE>   55


AVERAGE ANNUAL TOTAL RETURNS. The following table compares the Fund's R class
average annual returns for the periods ended December 31, 1998, to a broad-based
market benchmark.



<TABLE>
<CAPTION>
                                 1 YEAR                 5 YEARS                 10 YEARS
                                 ------                 -------                 --------
<S>                              <C>                    <C>                     <C>
Growth Fund R Class Shares       27.15%                 19.87%                   18.96%
S&P 500*                         28.57%                 24.06%                   19.21%
</TABLE>


- ---------------
*    The Standard and Poor's 500 Stock Index generally represents broad larger
capitalization equity market performance.


FEES AND EXPENSES: This section describes the fees and expenses that you may pay
if you buy and hold shares of the Fund.



SHAREHOLDER FEES. Fees paid directly from your investment.



<TABLE>
<CAPTION>
                                             CLASS A   CLASS B   CLASS C   CLASS I
                                             -------   -------   -------   -------
<S>                                          <C>       <C>       <C>       <C>
Maximum Sales Charge (Load) Imposed on
  Purchases (as % of offering price).......   5.75%     None      None      None
Maximum Deferred Sales Charge (Load) (as %
  of redemption proceeds)..................   None(1)   5.00%     1.00%     None
Maximum Sales Charge (Load) Imposed on
  Reinvested Dividends/Distributions.......   None      None      None      None
Redemption Fee(2) (as % of amount redeemed,
  if applicable)
  Shares held less than 180 days...........   1.00%     1.00%     1.00%     1.00%
  Shares held more than 180 days...........   None      None      None      None
Exchange Fee...............................   None      None      None      None
</TABLE>


- ---------------

(1)    The redemption of Class A shares purchased at net asset value under the
       Large Order NAV Purchase Privilege may be subject to a contingent
       deferred sales charge of 1.00% during the first year and 0.50% during the
       second year.



(2)    The redemption fee will be retained by the Fund. The redemption fee is
       designed to discourage short-term trading. The Fund discourages
       short-term investments in the Fund because they have a negative impact on
       remaining shareholders.



ANNUAL FUND OPERATING EXPENSES are paid out of the Fund's assets and include
fees for portfolio management, distribution services, maintenance of shareholder
accounts, shareholder servicing, accounting and other services. You do not pay
these fees directly but, as the example shows, these costs are borne indirectly
by shareholders.


  ANNUAL FUND OPERATING EXPENSES (expenses that are deducted from Fund assets)


<TABLE>
<CAPTION>
                                   CLASS A   CLASS B   CLASS C   CLASS I
                                   -------   -------   -------   -------
<S>                                <C>       <C>       <C>       <C>
Management Fee...................    .75%      .75%      .75%      .75%
Distribution (12b-1) and/or
  Service Fees...................    .25      1.00      1.00(1)   None
Other Expenses...................    .09       .09       .09       .09
                                    ----      ----      ----      ----
Total Annual Fund Operating
  Expenses.......................   1.09      1.84      1.84       .84
</TABLE>


- ---------------

(1)    Long-term shareholders may indirectly pay more than the equivalent of the
       maximum permitted front-end sales charge.


EXAMPLE: This example is intended to help you compare the cost of investing in
the Fund with the cost of investing in other mutual funds. The example assumes
that you invest $10,000 in the Fund for the time periods indicated and then
redeem all of your shares at the end of those periods. The example also assumes
that your investment has a 5% return each year and that the Fund's operating
expenses remain the same. Although your actual costs may be higher or lower,
based on these assumptions your costs would be:


<TABLE>
<CAPTION>
                       CLASS A     CLASS B       CLASS B        CLASS C       CLASS C      CLASS I
                       -------   -----------   ------------   -----------   ------------   -------
                                  (ASSUMING    (ASSUMING NO    (ASSUMING    (ASSUMING NO
                                 REDEMPTION)   REDEMPTION)    REDEMPTION)   REDEMPTION)
<S>                    <C>       <C>           <C>            <C>           <C>            <C>
1 Year...............  $  112      $  189         $             $  189         $           $   86
3 Years..............     348         584                          584                        269
5 Years..............     604       1,004                        1,004                        468
10 Years.............   1,334       2,173                        2,173                      1,040
</TABLE>



 4  William Blair Mutual Funds, Inc.  May 1, 1999, as supplemented September 30,
1999

<PAGE>   56

WILLIAM BLAIR VALUE DISCOVERY FUND                                       SUMMARY
- --------------------------------------------------------------------------------
INVESTMENT OBJECTIVE: The William Blair Value Discovery Fund seeks long-term
capital appreciation.

MAIN INVESTMENT STRATEGIES: The Fund invests primarily in a diversified
portfolio of the equity securities of small companies that the Adviser believes
offer a long-term investment value. In implementing its value discipline, the
Adviser evaluates the extent to which a company meets the following criteria:
(a) whether the company's current market value reflects a material discount from
the Adviser's estimate of the company's value, (b) whether the company has a
reasonable expectation of improving its level of profitability over a three-year
investment horizon, (c) whether the company has a capable and skilled management
team, (d) whether the company has a relatively strong capital structure, and (e)
whether there is a likelihood that the company will undergo a positive corporate
change within a three-year investment horizon. The weight that the Adviser gives
to each of the investment criteria depends upon the circumstances, and some of
the Fund's investments will not meet all of the criteria. The Fund is designed
for long-term investors.

MAIN RISKS OF INVESTING: Since the Fund invests most of its assets in equity
securities, the primary risk is that the value of the securities it holds might
decrease in response to the activities of an individual company or general
economic and market conditions. If this occurs, the Fund's net asset value may
also decrease. The securities of smaller companies may be more volatile and more
speculative than the securities of larger, more established issuers, which may
cause the Fund's share price to be more volatile. In addition, small companies
may be traded in low volumes. This can increase volatility and increase the risk
that the Fund will not be able to sell the security on short notice at a
reasonable price. Of course, the skill of the Adviser will play a significant
role in the Fund's ability to achieve its investment objective. The Fund's
returns will vary, and you could lose money by investing in the Fund.

FUND PERFORMANCE HISTORY


ANNUAL TOTAL RETURNS. The bar chart to the right provides an illustration of how
the Fund's performance has varied in each of the calendar years since the Fund
started. The Fund's past performance does not necessarily indicate how it will
perform in the future. The Class A, Class B, Class C and Class I shares are new
Classes of the Fund for which performance is not yet available. The Class R
shares of the Fund are offered in a separate prospectus. The returns for the
Class A, Class B, Class C and Class I shares will be substantially similar to
those of the Class R shares shown in the chart because all shares of the Fund
are invested in the same portfolio of securities. The annual returns of the
different Classes of shares will differ only to the extent that the expenses of
the Classes differ.

[FUND PERFORMANCE HISTORY CHART]


Class A, B and C share sale loads are not reflected in the above chart. If sales
loads were reflected, the Fund's returns would be less than those shown. Class I
has no sales loads.


HIGHEST AND LOWEST QUARTERLY RETURNS. During the period shown in the bar chart,
the highest return for a quarter was 26.58% (quarter ended 9/30/97) and the
lowest return for a quarter was -17.59% (quarter ended 9/30/98). Shareholders
should be aware that the Fund is a long-term investment and is not managed for
short-term results.


AVERAGE TOTAL RETURNS. The following table compares the Fund's R class average
annual returns for the periods ended December 31, 1998, indicated to a
broad-based securities market index.



<TABLE>
<CAPTION>
                                                      SINCE
                                                    INCEPTION
                                           1 YEAR   (12/23/96)
                                           ------   ----------
<S>                                        <C>      <C>
Value Discovery Fund R Class Shares         0.66%     15.91%
Russell 2000 Index*                        (2.55)%     9.20%
</TABLE>



May 1, 1999, as supplemented September 30, 1999                   Prospectus   5

<PAGE>   57

- ---------------

*    The Russell 2000 Index is a composite of the smallest 2000 stocks of the
     Russell 3000 Index, which consists of the largest 3000 stocks in the U.S.
     market as determined by market capitalization.


FEES AND EXPENSES: This table describes the fees and expenses that you may pay
if you buy and hold shares of the Fund.



SHAREHOLDER FEES. Fees paid directly from your investment.



<TABLE>
<CAPTION>
                                             CLASS A   CLASS B   CLASS C   CLASS I
                                             -------   -------   -------   -------
<S>                                          <C>       <C>       <C>       <C>
Maximum Sales Charge (Load) Imposed on
  Purchases (as % of offering price).......   5.75%     None      None      None
Maximum Deferred Sales Charge (Load) (as %
  of redemption proceeds)..................   None(1)   5.00%     1.00%     None
Maximum Sales Charge (Load) Imposed on
  Reinvested Dividends/ Distributions......   None      None      None      None
Redemption Fee(2) (as % of amount redeemed,
  if applicable)
  Shares held less than 180 days...........   1.00%     1.00%     1.00%     1.00%
  Shares held more than 180 days...........   None      None      None      None
Exchange Fee...............................   None      None      None      None
</TABLE>


- ---------------


(1)    The redemption of Class A shares purchased at net asset value under the
       Large Order NAV Purchase Privilege may be subject to a contingent
       deferred sales charge of 1.00% during the first year and 0.50% during the
       second year.



(2)    The redemption fee will be retained by the Fund. The redemption fee is
       designed to discourage short-term trading. The Fund discourages
       short-term investments in the Fund because they have a negative impact on
       remaining shareholders.


ANNUAL FUND OPERATING EXPENSES are paid out of the Fund's assets and include
fees for portfolio management, maintenance of shareholder accounts, shareholder
servicing, accounting and other services. You do not pay these fees directly
but, as the example shows, these costs are borne indirectly by shareholders.


  ANNUAL FUND OPERATING EXPENSES (expenses that are deducted from Fund assets)



<TABLE>
<CAPTION>
                                             CLASS A   CLASS B   CLASS C   CLASS I
                                             -------   -------   -------   -------
<S>                                          <C>       <C>       <C>       <C>
Management Fee.............................   1.15%     1.15%     1.15%     1.15%
Distribution (12b-1) and/or Service Fees...    .25      1.00      1.00(1)   None
Other Expenses.............................    .37       .37       .37       .37
                                              ----      ----      ----      ----
Total Annual Fund Operating Expenses.......   1.77      2.52      2.52      1.52
</TABLE>


- ---------------


(1)    Long-term shareholders may indirectly pay more than the equivalent of the
       maximum permitted front-end sales charge.


EXAMPLE: This example is intended to help you compare the cost of investing in
the Fund with the cost of investing in other mutual funds. The example assumes
that you invest $10,000 in the Fund for the time periods indicated and then
redeem all of your shares at the end of those periods. The example also assumes
that your investment has a 5% return each year and that the Fund's operating
expenses remain the same. Although your actual costs may be higher or lower,
based on these assumptions your costs would be:


<TABLE>
<CAPTION>
                           CLASS A     CLASS B       CLASS B        CLASS C       CLASS C      CLASS I
                           -------   -----------   ------------   -----------   ------------   -------
                                      (ASSUMING    (ASSUMING NO    (ASSUMING    (ASSUMING NO
                                     REDEMPTION)   REDEMPTION)    REDEMPTION)   REDEMPTION)
<S>                        <C>       <C>           <C>            <C>           <C>            <C>
1 Year...................  $  112      $  189         $             $  189         $           $   86
3 Years..................     348         584                          584                        269
5 Years..................     604       1,004                        1,004                        468
10 Years.................   1,334       2,173                        2,173                      1,040
</TABLE>



 6  William Blair Mutual Funds, Inc.  May 1, 1999, as supplemented September 30,
1999

<PAGE>   58

WILLIAM BLAIR INTERNATIONAL GROWTH FUND                                  SUMMARY
- --------------------------------------------------------------------------------
INVESTMENT OBJECTIVE: The William Blair International Growth Fund seeks
long-term capital appreciation through investment in well-managed, quality
growth companies.

MAIN INVESTMENT STRATEGIES: The Fund invests primarily in a diversified
portfolio of common stocks of foreign companies of all sizes. In choosing
investments, the Adviser performs fundamental company analysis. The Adviser
generally seeks common stocks of companies that historically have had and are
expected to maintain superior growth, profitability and quality relative to
local markets and relative to companies within the same industry worldwide.
Following stock selection, country selection and industry allocation are the
next most important investment criteria. The Adviser will vary the geographic
diversification and types of securities in which the Fund invests based upon its
continuous evaluation of economic, market and political trends throughout the
world. The Adviser normally will allocate the Fund's investments among at least
six different countries. Normally, the Fund's investments will be divided among
Continental Europe, the United Kingdom, Canada, Japan and the markets of the
Pacific Basin. However, selective investments may also be made in Latin America
and in emerging markets, which include every country in the world except the
United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and
most Western European countries. The Fund is designed for long-term investors.

MAIN RISKS OF INVESTING: Because the Fund invests most of its assets in common
stocks, the primary risk is that the value of the stocks it holds might decrease
in response to the activities of those companies or market and economic
conditions. If this occurs, the Fund's net asset value may also decrease.
Foreign investments often involve additional risks, including political
instability, differences in financial reporting standards, and less stringent
regulation of securities markets. These risks are magnified in less-established,
emerging markets. Because the securities held by the Fund usually will be
denominated in currencies other than the U.S. dollar, changes in foreign
currency exchange rates may adversely affect the value of the Fund's
investments. In addition, the Fund may invest in the securities of small
companies, which may be more volatile and less liquid than securities of large
companies. Of course, the skill of the Adviser will play a significant role in
the Fund's ability to achieve its investment objective. The Fund's returns will
vary, and you could lose money by investing in the Fund.

FUND PERFORMANCE HISTORY


ANNUAL TOTAL RETURNS. The bar chart to the right provides an illustration of how
the Fund's performance has varied in each calendar year since the Fund started.
The Fund's past performance does not necessarily indicate how it will perform in
the future. The Class A, Class B, Class C and Class I shares are new Classes of
the Fund for which performance is not yet available. The Class R shares of the
Fund are offered in a separate prospectus. The returns for the Class A, Class B,
Class C and Class I shares will be substantially similar to those of the Class R
shares shown in the chart because all shares of the Fund are invested in the
same portfolio of securities. The annual returns of the different Classes of
shares will differ only to the extent that the expenses of the Classes differ.

[FUND PERFORMANCE HISTORY CHART]


Class A, B and C share sale loads are not reflected in the above chart. If sales
loads were reflected, the Fund's returns would be less than those shown. Class I
has no sales loads.



HIGHEST AND LOWEST QUARTERLY RETURNS. During the period shown in the bar chart,
the highest return for a quarter was 17.43% (quarter ended 3/31/98) and the
lowest return for a quarter was -16.70% (quarter ended 9/30/98). Shareholders
should be aware that the Fund is a long-term investment and is not managed for
short-term results.



May 1, 1999, as supplemented September 30, 1999                   Prospectus   7

<PAGE>   59

AVERAGE ANNUAL TOTAL RETURNS. The table compares the Fund's average annual total
returns for the periods indicated to a broad-based securities market index.


<TABLE>
<CAPTION>
                                                         SINCE INCEPTION
                                      1 YEAR   5 YEARS      (10/1/92)
                                      ------   -------   ---------------
<S>                                   <C>      <C>       <C>
International Growth Fund R Class
  Shares                              11.46%    7.37%        11.10%
Morgan Stanley Int'l Index*           14.46%    7.87%        10.91%
</TABLE>


- ---------------

*    The Morgan Stanley Capital International All Country World Free except U.S.
     Index includes developed and emerging markets and reduces the Japanese
     portion, making it comparable to the International Growth Fund in terms of
     investment approach.


FEES AND EXPENSES: This section describes the fees and expenses that you may pay
if you buy and hold shares of the Fund.



SHAREHOLDER FEES. Fees paid directly from your investment.



<TABLE>
<CAPTION>
                                             CLASS A   CLASS B   CLASS C   CLASS I
                                             -------   -------   -------   -------
<S>                                          <C>       <C>       <C>       <C>
Maximum Sales Charge (Load) Imposed on
  Purchases (as % of offering price).......   5.75%     None      None      None
Maximum Deferred Sales Charge (Load) (as %
  of redemption proceeds)..................   None(1)   5.00%     1.00%     None
Maximum Sales Charge (Load) Imposed on
  Reinvested Dividends/ Distributions......   None      None      None      None
Redemption Fee(2) (as % of amount redeemed,
  if applicable)
  Shares held less than 180 days...........   1.00%     1.00%     1.00%     1.00%
  Shares held more than 180 days...........   None      None      None      None
Exchange Fee...............................   None      None      None      None
</TABLE>


- ---------------


(1)    The redemption of Class A shares purchased at net asset value under the
       Large Order NAV Purchase Privilege may be subject to a contingent
       deferred sales charge of 1.00% during the first year and 0.50% during the
       second year.



(2)    The redemption fee will be retained by the Fund. The redemption fee is
       designed to discourage short-term trading. The Fund discourages
       short-term investments in the Fund because they have a negative impact on
       remaining shareholders.


ANNUAL FUND OPERATING EXPENSES are paid out of the Fund's assets and include
fees for portfolio management, maintenance of shareholder accounts, shareholder
servicing, accounting and other services. You do not pay these fees directly
but, as the example shows, these costs are borne indirectly by shareholders.


  ANNUAL FUND OPERATING EXPENSES (expenses that are deducted from Fund assets)



<TABLE>
<CAPTION>
                                             CLASS A   CLASS B   CLASS C   CLASS I
                                             -------   -------   -------   -------
<S>                                          <C>       <C>       <C>       <C>
Management Fee.............................   1.10%     1.10%     1.10%     1.10%
Distribution (12b-1) and/or Service Fees...    .25      1.00      1.00(1)   None
Other Expenses.............................    .26       .26       .26       .26
                                              ----      ----      ----      ----
Total Annual Fund Operating Expenses.......   1.61      2.36      2.36      1.36
                                              ====      ====      ====      ====
</TABLE>


- ---------------


(1)    Long-term shareholders may indirectly pay more than the equivalent of the
       maximum permitted front-end sales charge.



 8  William Blair Mutual Funds, Inc.  May 1, 1999, as supplemented September 30,
1999

<PAGE>   60

EXAMPLE: This example is intended to help you compare the cost of investing in
the Fund with the cost of investing in other mutual funds. The example assumes
that you invest $10,000 in the Fund for the time periods indicated and then
redeem all of your shares at the end of those periods. The example also assumes
that your investment has a 5% return each year and that the Fund's operating
expenses remain the same. Although your actual costs may be higher or lower,
based on these assumptions your cost would be:


<TABLE>
<CAPTION>
                       CLASS A     CLASS B       CLASS B        CLASS C       CLASS C      CLASS I
                       -------   -----------   ------------   -----------   ------------   -------
                                  (ASSUMING    (ASSUMING NO    (ASSUMING    (ASSUMING NO
                                 REDEMPTION)   REDEMPTION)    REDEMPTION)   REDEMPTION)
<S>                    <C>       <C>           <C>            <C>           <C>            <C>
1 Year...............  $  112      $  189         $             $  189         $           $   86
3 Years..............     348         584                          584                        269
5 Years..............     604       1,004                        1,004                        468
10 Years.............   1,334       2,173                        2,173                      1,040
</TABLE>



May 1, 1999, as supplemented September 30, 1999                   Prospectus   9

<PAGE>   61

WILLIAM BLAIR EMERGING MARKETS GROWTH FUND                               SUMMARY
- --------------------------------------------------------------------------------
INVESTMENT OBJECTIVE: The William Blair Emerging Markets Growth Fund seeks
long-term capital appreciation.

MAIN INVESTMENT STRATEGIES: The Fund invests primarily in a diversified
portfolio of equity securities issued by companies in emerging markets. In
choosing investments, the Adviser first analyzes individual companies. The
Adviser generally seeks well-managed companies with superior business
fundamentals, including global leadership in product quality or cost
competitiveness, dominant or improving market position within a growing local or
regional economy, and sustainable above-average and/or increasing returns on
invested capital. Following stock selection, the Adviser allocates investments
based upon its analysis of the economic strength of various countries and
industries. The Adviser normally will allocate the Fund's investments among at
least six different countries. Currently, emerging markets include every country
in the world other than the United States, Canada, Japan, Australia, New
Zealand, Hong Kong, Singapore and most Western European countries. The Fund is
designed for long-term investors.

MAIN RISKS OF INVESTING: Because the Fund invests most of its assets in equity
securities of companies, the primary risk is that value of the securities it
holds might decrease in response to the activities of those companies or markets
and economic conditions. If this occurs, the Fund's net asset value may also
decrease. Foreign investments often involve additional risks, such as political
instability, differences in financial reporting standards and less stringent
regulation of securities markets. These risks may be greatly increased in
emerging market countries because the securities in emerging markets may be
subject to greater volatility and less liquidity than companies in more
developed markets. Because the securities held by the Fund usually will be
denominated in currencies other than the U.S. dollar, changes in foreign
currency exchange rates may adversely affect the value of the Fund's
investments. The currencies of certain emerging market countries have
experienced a steady devaluation relative to the U.S. dollar, and continued
devaluations may adversely affect the value of the Fund's assets denominated in
such currencies. Many emerging markets have experienced substantial rates of
inflation for many years, and continued inflation may adversely affect the
economies and securities markets of such countries. The Fund also may invest in
the securities of small companies, which may be more volatile and less liquid
than securities of large companies. Of course, the skill of the Adviser will
play a significant role in the Fund's ability to achieve its investment
objective. The Fund's returns will vary, and you could lose money by investing
in the Fund.


FEES AND EXPENSES: This section describes the fees and expenses that you may pay
if you buy and hold shares of the Fund.



 10  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   62


SHAREHOLDER FEES. Fees paid directly from your investment.



<TABLE>
<CAPTION>
                                             CLASS A   CLASS B   CLASS C   CLASS I
                                             -------   -------   -------   -------
<S>                                          <C>       <C>       <C>       <C>
Maximum Sales Charge (Load) Imposed on
  Purchases (as % of offering price).......   5.75%     None      None      None
Maximum Deferred Sales Charge (Load) (as %
  of redemption proceeds)..................   None(1)   5.00%     1.00%     None
Maximum Sales Charge (Load) Imposed on
  Reinvested Dividends/ Distributions......   None      None      None      None
Redemption Fee(2) (as % of amount redeemed,
  if applicable)
  Shares held less than 180 days...........   1.00%     1.00%     1.00%     1.00%
  Shares held more than 180 days...........   None      None      None      None
Exchange Fee...............................   None      None      None      None
</TABLE>


- ---------------

(1)    The redemption of Class A shares purchased at net asset value under the
       Large Order NAV Purchase Privilege may be subject to a contingent
       deferred sales charge of 1.00% during the first year and 0.50% during the
       second year.



(2)    The redemption fee will be retained by the Fund. The redemption fee is
       designed to discourage short-term trading. The Fund discourages
       short-term investments in the Fund because they have a negative impact on
       remaining shareholders.


ANNUAL FUND OPERATING EXPENSES are paid out of the Fund's assets and include
fees for portfolio management, maintenance of shareholder accounts, shareholder
servicing, accounting and other services. You do not pay these fees directly
but, as the example shows, these costs are borne indirectly by shareholders.


  ANNUAL FUND OPERATING EXPENSES (expenses that are deducted from Fund assets)



<TABLE>
<CAPTION>
                                             CLASS A   CLASS B   CLASS C   CLASS I
                                             -------   -------   -------   -------
<S>                                          <C>       <C>       <C>       <C>
Management Fee.............................   1.40%     1.40%     1.40%     1.40%
Distribution (12b-1) and/or Service Fees...    .25      1.00      1.00(1)   None
Other Expenses.............................   4.95      4.95      4.95      4.95
                                              ----      ----      ----      ----
Total Annual Fund Operating Expenses(2)....   6.60      7.35      7.35      6.35
                                              ====      ====      ====      ====
</TABLE>


- ---------------


(1)    Long-term shareholders may indirectly pay more than the equivalent of the
       maximum permitted front-end sales charge.


(2)    Due to the Adviser voluntarily waiving fees and absorbing expenses, the
       Fund's actual total expenses were 2.25% (annualized) during 1998. The
       Adviser intends to voluntarily cap the Fund's expenses at 2.25%
       indefinitely.


EXAMPLE: This example is intended to help you compare the cost of investing in
the Fund with the cost of investing in other mutual funds. The example assumes
that you invest $10,000 in the Fund for the time periods indicated and then
redeem all of your shares at the end of those periods. The example also assumes
that your investment has a 5% return each year and that the Fund's operating
expenses remain the same. Although your actual costs may be higher or lower,
based on these assumptions your costs would be:


<TABLE>
<CAPTION>
                       CLASS A*    CLASS B*       CLASS B*      CLASS C*       CLASS C*     CLASS I*
                       --------   -----------   ------------   -----------   ------------   --------
                                   (ASSUMING    (ASSUMING NO    (ASSUMING    (ASSUMING NO
                                  REDEMPTION)   REDEMPTION)    REDEMPTION)   REDEMPTION)
<S>                    <C>        <C>           <C>            <C>           <C>            <C>
1 Year...............   $  256      $  333        $              $  333        $             $  231
3 Years..............      788       1,016                        1,016                         711
5 Years..............    1,345       1,722                        1,722                       1,217
10 Years.............    2,863       3,593                        3,593                       2,607
</TABLE>


- ---------------

*    With the expense cap, the Fund's operating expenses would be as follows:

     1 Year: $112, $189, $189 and $86 for Class A, B, C and I, respectively;


     3 Years: $348, $584, $584, $269 for Class A, B, C and I, respectively;


     5 Years: $604, $1,004, $1,004, and $468 for Class A, B, C and I,
     respectively;


     10 Years: $1,334, $2,173, $2,173 and $1,040 for Class A, B, C and I,
     respectively.



May 1, 1999, as supplemented September 30, 1999                  Prospectus   11

<PAGE>   63

WILLIAM BLAIR INCOME FUND                                                SUMMARY
- --------------------------------------------------------------------------------
INVESTMENT OBJECTIVE: The William Blair Income Fund seeks to provide investors
with as high a level of current income as is consistent with the preservation of
capital by investing primarily in a diversified portfolio of high-grade,
intermediate-term debt securities.

MAIN INVESTMENT STRATEGIES: The Fund invests primarily in a diversified
portfolio of intermediate-term income-producing securities, including government
securities, U.S. dollar-denominated corporate bonds and notes, collateralized
obligations and money market instruments that are rated in one of the top three
categories. The Fund's investments are subject to certain maturity and duration
restrictions, by which the Fund seeks to approximate the total returns of an
intermediate-term debt index while also providing investors with the additional
security of shorter-term obligations. The Adviser continually considers the
Fund's exposure to interest rate risk because, if interest rates increase, the
Fund's yield may increase and the market value of the Fund's securities will
likely decrease, which would cause the Fund's net asset value and total return
to go down. If interest rates decrease, the Fund's yield may decrease and the
market value of the Fund's securities may increase, which would likely increase
the Fund's net asset value and total return.

MAIN RISKS OF INVESTING: The primary risk of investing in the Fund is interest
rate risk. The yield paid by the Fund will vary with changes in interest rates.
As noted above, changes in interest rates may cause changes in the Fund's yield,
net asset value and total return. Investments with longer maturities, which
typically provide higher yield than securities with shorter maturities, may
subject the Fund to increased price changes resulting from market yield
fluctuations. The Fund is also subject to credit risk. The Fund's net asset
value and total return may be adversely affected by the inability of the issuers
of the Fund's securities to make payment at maturity. Of course, the skill of
the Adviser will play a significant role in the Fund's ability to achieve its
investment objective. The Fund's returns will vary, and you could lose money by
investing in the Fund.

FUND PERFORMANCE HISTORY


ANNUAL TOTAL RETURNS. The bar chart below provides an illustration of how the
Fund's performance has varied in each of the last 10 calendar years. The Fund's
past performance does not necessarily indicate how it will perform in the
future. The Class A, Class B, Class C and Class I shares are new Classes of the
Fund for which performance is not yet available. The Class R shares of the Fund
are offered in a separate prospectus. The returns for the Class A, Class B,
Class C and Class I shares will be substantially similar to those of the Class R
shares shown in the chart below because all shares of the Fund are invested in
the same portfolio of securities. The annual returns of the different Classes of
shares will differ only to the extent that the expenses of the Classes differ.



Class A, B and C share sale loads are not reflected in the above chart. If sales
loads were reflected, the Fund's returns would be less than those shown. Class I
has no sales loads.

                        [FUND PERFORMANCE HISTORY CHART]


HIGHEST AND LOWEST QUARTERLY RETURNS. During the period shown in the bar chart,
the highest return for a quarter was 5.44% (quarter ended 12/31/91) and the
lowest return for a quarter was -1.30% (quarter ended 12/31/92).



 12  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   64


AVERAGE ANNUAL TOTAL RETURNS. The following table compares the Fund's average
annual returns for the periods ended December 31, 1998, to a broad-based
securities market index.



<TABLE>
<CAPTION>
                                                              SINCE INCEPTION
                                           1 YEAR   5 YEARS      (9/25/90)
                                           ------   -------   ---------------
<S>                                        <C>      <C>       <C>
Income Fund Class R Shares                  7.07%    6.22%         7.90%
Lehman Intermediate Gov't/Corp. Index*      8.44%    6.60%         8.19%
</TABLE>


- ---------------

 *     The Lehman Intermediate Government/Corporate Index represents broad
       intermediate government/corporate bond market performance.


YIELD: You may obtain the most current yield information for the Fund by calling
1-800-742-7272.


FEES AND EXPENSES: This section describes the fees and expenses that you may pay
if you buy and hold shares of the Fund.



SHAREHOLDER FEES. Fees paid directly from your investment.



<TABLE>
<CAPTION>
                                                           CLASS A   CLASS B   CLASS C   CLASS I
                                                           -------   -------   -------   -------
<S>                                                        <C>       <C>       <C>       <C>
Maximum Sales Charge (Load) Imposed on Purchases (as % of
  offering price)........................................   2.00%     None      None      None
Maximum Deferred Sales Charge (Load) (as % of redemption
  proceeds)..............................................   None(1)   2.00%     1.00%     None
Maximum Sales Charge (Load) Imposed on Reinvested
  Dividends/ Distributions...............................   None      None      None      None
Redemption Fee(2) (as % of amount redeemed, if
  applicable)
  Shares held less than 180 days.........................   1.00%     1.00%     1.00%     1.00%
  Shares held more than 180 days.........................   None      None      None      None
Exchange Fee.............................................   None      None      None      None
</TABLE>


- ---------------

(1)    The redemption of Class A shares purchased at net asset value under the
       Large Order NAV Purchase Privilege may be subject to a contingent
       deferred sales charge of .25% during the first year.



(2)    The redemption fee will be retained by the Fund. The redemption fee is
       designed to discourage short-term trading. The Fund discourages
       short-term investments in the Fund because they have a negative impact on
       remaining shareholders.


ANNUAL FUND OPERATING EXPENSES are paid out of the Fund's assets and include
fees for portfolio management, maintenance of shareholder accounts, shareholder
servicing, accounting and other services. You do not pay these fees directly
but, as the example shows, these costs are borne indirectly by shareholders.


  ANNUAL FUND OPERATING EXPENSES (expenses that are deducted from Fund assets)



<TABLE>
<CAPTION>
                                                 CLASS A   CLASS B   CLASS C   CLASS I
                                                 -------   -------   -------   -------
<S>                                              <C>       <C>       <C>       <C>
Management Fee.................................    .59%      .59%      .59%      .59%
Distribution (12b-1) and/or Service Fees.......    .25      1.00      1.00(1)   None
Other Expenses.................................    .12       .12       .12       .12
                                                   ---      ----      ----      ----
Total Annual Fund Operating Expenses...........    .96      1.71      1.71       .71
                                                   ===      ====      ====      ====
</TABLE>


- ---------------

(1)    Long-term shareholders may indirectly pay more than the equivalent of the
       maximum permitted front-end sales charge.


EXAMPLE: This example is intended to help you compare the cost of investing in
the Fund with the cost of investing in other mutual funds. The example assumes
that you invest $10,000 in the Fund for the time periods indicated and then
redeem all of your shares at the end of those periods. The example also assumes
that your investment has a 5%


May 1, 1999, as supplemented September 30, 1999                  Prospectus   13

<PAGE>   65

return each year and that the Fund's operating expenses remain the same.
Although your actual costs may be higher or lower, based on these assumptions
your costs would be:


<TABLE>
<CAPTION>
                       CLASS A     CLASS B       CLASS B        CLASS C       CLASS C      CLASS I
                       -------   -----------   ------------   -----------   ------------   -------
                                  (ASSUMING    (ASSUMING NO    (ASSUMING    (ASSUMING NO
                                 REDEMPTION)   REDEMPTION)    REDEMPTION)   REDEMPTION)
<S>                    <C>       <C>           <C>            <C>           <C>            <C>
1 Year...............  $  112      $  189         $             $  189         $           $   86
3 Years..............     348         584                          584                        269
5 Years..............     604       1,004                        1,004                        468
10 Years.............   1,334       2,173                        2,173                      1,040
</TABLE>



 14  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   66

WILLIAM BLAIR READY RESERVES FUND                                        SUMMARY
- --------------------------------------------------------------------------------
INVESTMENT OBJECTIVE: The William Blair Ready Reserves Fund seeks to obtain the
maximum current income consistent with preservation of capital by investing
exclusively in high-quality money market instruments.

MAIN INVESTMENT STRATEGIES: The Fund invests exclusively in short-term U.S.
dollar-denominated domestic and foreign money market instruments, which include
securities issued by domestic and foreign corporations; the U.S. Government, its
agencies and instrumentalities; U.S. and foreign banks; foreign governments; and
multinational organizations (e.g. the World Bank). The Fund invests exclusively
in securities that are high-quality, which means that they are rated in the top
2 categories. These instruments are considered to be among the safest
investments available because of their short maturities, liquidity and
high-quality ratings. The Fund is designed to be highly liquid and seeks to
maintain a net asset value of $1.00 per share. The Fund is designed for
investors who seek to obtain the maximum current income consistent with the
preservation of capital.

MAIN RISKS OF INVESTING: Although the Fund seeks to preserve the value of your
investment at $1.00 per share, it is possible to lose money by investing in the
Fund. As with any money market fund, there is a low risk that the issuers or
guarantors of securities will default on the payment of principal or interest or
the obligation to repurchase securities from the Fund. An investment in the Fund
is not insured or guaranteed by the Federal Deposit Insurance Corporation or any
other government agency. Of course, the skill of the Adviser will play a
significant role in the Fund's ability to achieve its investment objective.

FUND PERFORMANCE HISTORY

ANNUAL TOTAL RETURNS. The bar chart below provides an illustration of how the
Fund's performance has varied in each of the last 10 calendar years. The Fund's
past performance does not necessarily indicate how it will perform in the
future.
                        [FUND PERFORMANCE HISTORY CHART]

HIGHEST AND LOWEST QUARTERLY RETURNS. During the period shown in the bar chart,
the highest return for a quarter was 9.02% (quarter ended June 30, 1989) and the
lowest return for a quarter was 2.55% (quarter ended June 30, 1993).


AVERAGE ANNUAL TOTAL RETURNS. The following table compares the Fund's average
annual total returns for the periods ended December 31, 1998, to a broad-based
securities market index.


<TABLE>
<CAPTION>
                                        1 YEAR   5 YEARS   10 YEARS
                                        ------   -------   --------
<S>                                     <C>      <C>       <C>
Ready Reserves Fund                      4.98%    4.77%      5.22%
S&P-rated AAA*                           4.97%    4.75%      5.20%
</TABLE>

- ---------------
*    The Standard and Poor's-rated AAA Money Market Funds Index includes money
     market mutual funds rated AAA by Standard and Poor's.

YIELD: You may obtain the most current yield information for the Fund by calling
1-800-742-7272.


FEES AND EXPENSES: This section describes the fees and expenses that you may pay
if you buy and hold shares of the Fund.



May 1, 1999, as supplemented September 30, 1999                  Prospectus   15

<PAGE>   67


SHAREHOLDER FEES. All William Blair Mutual Funds are no-load investments, so you
will not pay any shareholder fees when you buy or sell shares of the Fund. When
you present a check to redeem shares in excess of the value of the account or
for an amount less than $500, the Fund may charge your account a $25 fee.


ANNUAL FUND OPERATING EXPENSES are paid out of the Fund's assets and include
fees for portfolio management, maintenance of shareholder accounts, shareholder
servicing, accounting and other services. You do not pay these fees directly
but, as the example shows, these costs are borne indirectly by shareholders.


  ANNUAL FUND OPERATING EXPENSES (expenses that are deducted from Fund assets)

<TABLE>
<S>                                                           <C>
Management Fee..............................................  .59%
Other Expenses..............................................  .10%
                                                              ----
Total Annual Fund Operating Expenses........................  .69%
</TABLE>


EXAMPLE: This example is intended to help you compare the cost of investing in
the Fund with the cost of investing in other mutual funds. The example assumes
that you invest $10,000 in the Fund for the time periods indicated and then
redeem all of your shares at the end of those periods. The example also assumes
that your investment has a 5% return each year and that the Fund's operating
expenses remain the same. Although your actual costs may be higher or lower,
based on these assumptions your costs would be:


<TABLE>
<CAPTION>
1 YEAR   3 YEARS   5 YEARS   10 YEARS
- ------   -------   -------   --------
<S>      <C>       <C>       <C>
 $71      $221      $385       $861
</TABLE>


FINANCIAL HIGHLIGHTS: The table below is intended to help you understand the
Fund's financial performance for the past several years. The total return
figures show what an investor in the Fund would have earned (or lost) assuming
reinvestment of all dividends and distributions. This information has been
audited by Ernst & Young LLP, whose report, along with the Fund's financial
statement, is included in the annual report, which is available upon request
(see back cover).

<TABLE>
<CAPTION>
                                                          YEARS ENDED DECEMBER 31
                                           ------------------------------------------------------
                                              1998        1997       1996       1995       1994
                                           ----------   --------   --------   --------   --------
<S>                                        <C>          <C>        <C>        <C>        <C>
Net asset value, beginning of year.......  $     1.00   $   1.00   $   1.00   $   1.00   $   1.00
Income from investment operations:
  Net investment income..................         .05        .05        .05        .05        .04
  Net realized and unrealized gain (loss)
     on investments......................          --         --         --         --       (.01)
                                           ----------   --------   --------   --------   --------
          Total from investment
            operations...................         .05        .05        .05        .05        .03
Less distributions from:
  Net investment income..................         .05        .05        .05        .05        .04
                                           ----------   --------   --------   --------   --------
  Total distributions....................         .05        .05        .05        .05        .04
                                           ----------   --------   --------   --------   --------
Capital contribution.....................          --         --         --         --        .01
                                           ----------   --------   --------   --------   --------
Net asset value, end of year.............  $     1.00   $   1.00   $   1.00   $   1.00   $   1.00
                                           ==========   ========   ========   ========   ========
Total return (%).........................        4.98       5.04       4.81       5.45       3.67(a)
Ratios to average net assets (%):
  Expenses...............................         .69        .70        .71        .72        .71
  Net investment income..................        4.87       4.92       4.78       5.30       3.61
Supplemental data:
  Net assets at end of year (000s).......  $1,189,051   $904,569   $760,808   $703,993   $521,277
</TABLE>

- ---------------


(a)    The total return includes the effect of the investment adviser's capital
       contribution. Without the investment adviser's capital contribution, the
       total return would have been 3.40%.



 16  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   68

        INVESTMENT OBJECTIVES, PRINCIPAL INVESTMENT STRATEGIES AND RISKS
- --------------------------------------------------------------------------------
Each Fund is a series of William Blair Mutual Funds, Inc., an open-end
management investment company. William Blair & Company, L.L.C. (the "Adviser")
provides management and investment advisory services to the Funds.

The following section takes a closer look at the investment objectives of each
Fund, its principal investment strategies and certain related investment risks.
Each Fund's secondary strategies or investments are described in the Investment
Glossary at the end of this prospectus. In addition, the Statement of Additional
Information contains more detailed information about certain of these practices,
the potential risks and/or the limitations adopted by each Fund to help manage
such risks.

All investments, including those in mutual funds, have risks. No investment is
suitable for all investors. The Growth Fund, Value Discovery Fund, International
Growth Fund and Emerging Markets Growth Fund are intended for long-term
investors. In addition, the International Growth Fund and Emerging Markets
Growth Fund are intended for investors who can accept the risks entailed in
investing in foreign securities. Of course, there can be no assurance that a
Fund will achieve its objective.


May 1, 1999, as supplemented September 30, 1999                  Prospectus   17

<PAGE>   69

GROWTH FUND
- --------------------------------------------------------------------------------
GOAL AND STRATEGY

The Growth Fund seeks long-term appreciation of capital by investing in
well-managed companies in growing industries. The Fund invests primarily in a
diversified portfolio of the common stocks and equity-related securities of
domestic companies.

INVESTMENT PROCESS

The Adviser researches the market for companies that have grown more rapidly
than the gross national product from one business cycle to the next. The Fund
may invest in cyclical industries when the Adviser deems them to be at or near
the bottom of their business cycle and expects a multi-year period of sustained
growth. The Adviser seeks growth opportunities by investing in the following
classes of companies in varying proportions:

       LARGE, high quality, seasoned growth companies that have demonstrated
       sustained growth over a long period of time;

       MEDIUM-sized companies of recognized investment quality whose records of
       sales and earnings growth are not as well established; and

       SMALL, emerging, rapid-growth companies that have had especially vigorous
       growth in revenues and earnings.

The Adviser will invest in companies that it believes are well-managed
considering some or all of the following investment criteria:

       A LEADER IN THE FIELD. The company should be, or clearly have the
       expectation of becoming, a significant provider in the primary markets it
       serves.

       UNIQUE OR SPECIALTY COMPANY. The company should have some distinctive
       attribute that cannot easily be duplicated by present or potential
       competitors. This may take the form of proprietary products or processes,
       a unique distribution system, an entrenched brand name or an especially
       strong financial position.

       QUALITY PRODUCTS OR SERVICES. The company's products or services should
       be regarded as being of superior quality, which should enable the company
       to obtain a premium price and to command greater customer loyalty.

       MARKETING CAPABILITY. The company should have a distinctive capability in
       sales, service or distribution.

       VALUE TO CUSTOMER. The prices of the company's products or services
       should be based upon their value to the customer, rather than their
       production cost.

       RETURN ON EQUITY. The company should have achieved, or have the potential
       to achieve, an above-average return on equity through efficient use of
       assets and adequate margins, rather than excessive financial leverage.
       Such companies should be able to finance most or all of their growth
       internally and translate revenue and income growth into rising per share
       earnings and dividends.

       CONSERVATIVE FINANCIAL POLICIES AND ACCOUNTING PRACTICES. The company
       should have a relatively simple, clean financial structure and adhere to
       conservative and straightforward accounting practices.

PORTFOLIO SECURITIES

The Fund invests primarily in a diversified portfolio of the common stocks of
domestic companies and related equity securities. To a limited extent, the Fund
may invest in depository receipts, illiquid securities, investment companies,
when-issued and delayed delivery securities and repurchase agreements which are
described in the Investment Glossary at the end of this prospectus. The
Investment Glossary also describes the Fund's policies with regard to borrowing,
concentration, diversification and portfolio turnover. The Fund may invest to a
limited extent in warrants, which are described in the Statement of Additional
Information.


 18  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   70

INVESTMENT RISKS

Because the Fund invests substantially all of its assets in common stocks, the
main risk is that the value of the stocks it holds may decrease in response to
the activities of an individual company or in response to general market,
business and economic conditions. If this occurs, the Fund's share price may
also decrease. Stocks of smaller companies involve greater risk than those of
larger, more established companies. This is because smaller companies may be in
earlier stages of development, may be dependent on a small number of products or
services, may lack substantial capital reserves and/or do not have proven track
records. Smaller companies may be more adversely affected by poor economic or
market conditions, and may be traded in low volumes, which may increase
volatility and liquidity risks. The Fund is not intended to be a complete
investment program and there is no assurance that its investment objective can
be achieved.

Generally, the Fund will remain fully invested, and the Adviser will not attempt
to time the market. However, if a significant adverse market action is
anticipated, investment-grade debt securities may be held without limit as a
temporary defensive measure. Normally, the Fund does not purchase any stocks
with a view to quick turnover for capital gains. When the Fund is invested
defensively, it may not achieve its investment objective.

PORTFOLIO MANAGEMENT

The Growth Fund is co-managed by Rocky Barber and Mark A. Fuller, III.

Rocky Barber, a principal of William Blair & Company, L.L.C., has co-managed the
Fund since 1992. He joined William Blair in 1986 as a portfolio manager and
manager of the Investment Management Department. In addition to his management
responsibilities, he is a member of the department's Growth team. Previously, he
was an equity and fixed-income manager with Alliance Capital Management for nine
years and president of the Alliance Capital Bond Fund, a group of fixed-income
mutual funds. Rocky is president of William Blair Mutual Funds, Inc. and a past
Chairman of the Board of Trustees of the Stanford Business School Trust. He
currently serves on the Board of the LaRabida Children's Hospital Foundation and
is a member of the Investment Analysts Society of Chicago. Education: B.A., M.S.
and M.B.A., Stanford University; and CFA.

Mark A. Fuller, III, a principal of William Blair & Company, L.L.C., has
co-managed the Fund since 1992. He has been with William Blair since 1983. He
began his career in Institutional Sales, developing long-standing relationships
with each of the firm's research analysts. He is a portfolio manager for
numerous accounts and is a member of the department's Small Cap and Aggressive
Growth teams. Prior to joining William Blair, he was a sales representative with
IBM Corporation. Education: B.A., Northwestern University; M.B.A., Northwestern
University Kellogg Graduate School of Management.


May 1, 1999, as supplemented September 30, 1999                  Prospectus   19

<PAGE>   71

VALUE DISCOVERY FUND
- --------------------------------------------------------------------------------
GOAL AND STRATEGY

The Value Discovery Fund's objective is to seek long-term capital appreciation.
The Fund pursues its objective by investing with a value discipline primarily in
a diversified portfolio of the equity securities of small companies.

INVESTMENT PROCESS

In selecting companies for investment, the Adviser evaluates the extent to which
a company meets the investment criteria set forth below. The weight given to a
particular investment criterion will depend upon the circumstances, and some
Fund holdings may not meet all of the following criteria, which are described
more fully in the Statement of Additional Information:

       MATERIAL PRICE/VALUE DISPARITY--whether the company's current market
       value reflects a material discount from the Adviser's estimate of the
       company's intrinsic value.

       PROBABLE EXPANSION IN PROFITABILITY--whether the company has a reasonable
       expectation of improving its level of profitability over a three-year
       investment horizon.

       SKILLED AND COMMITTED MANAGEMENT--whether the company has a capable and
       skilled management team and a clearly articulated and logical business
       strategy with a reasonable probability of successful execution.

       STRONG CAPITAL STRUCTURE--whether the company has a relatively simple,
       clean financial structure without excessive use of financial leverage. In
       addition, the company should adhere to conservative and straightforward
       accounting practices.

       POSITIVE CATALYST--the likelihood that the company will undergo a
       positive corporate change within a three-year investment horizon.

PORTFOLIO SECURITIES

Generally, most of the Fund's assets will be invested in the common stocks of
small companies. The Fund may also hold debentures and preferred stocks if they
are convertible into common stocks that meet the Fund's investment criteria. The
Fund may invest up to 15% of its net assets in foreign securities, which may
include American Depository Receipts or substantially similar investments;
however, the Fund may invest only up to 5% of its net assets directly in foreign
securities. To a limited extent, the Fund may invest in depository receipts,
foreign securities, illiquid securities, investment companies, real estate
investment trusts, repurchase agreements and when-issued and delayed delivery
securities which are described in the Investment Glossary at the end of this
prospectus. The Investment Glossary also describes the Fund's policies with
regard to borrowing, concentration, diversification and portfolio turnover. The
Fund may invest to a limited extent in warrants and futures, which are described
in the Statement of Additional Information.


 20  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   72

INVESTMENT RISKS

Because the Fund invests substantially all of its assets in common stocks, the
main risk is that the value of the stocks it holds may decrease in response to
the activities of an individual company or in response to general market,
business and economic conditions. If this occurs, the Fund's share price may
also decrease. Stocks of smaller companies involve greater risk than those of
larger, more established companies. This is because smaller companies may be in
earlier stages of development, may be dependent on a small number of products or
services, may lack substantial capital reserves and/or do not have proven track
records. Smaller companies may be more adversely affected by poor economic or
market conditions, and may be traded in low volumes, which may increase
volatility and liquidity risks. From time to time, the Fund may invest in the
equity securities of very small companies, often referred to as "micro-cap"
companies. The considerations noted above are generally intensified for these
investments. Any convertible debentures issued by small companies are likely to
be lower-rated or non-rated securities, which generally involve more credit risk
than debentures in the higher rating categories and generally include some
speculative characteristics, including uncertainties or exposure to adverse
business, financial or economic conditions which could lead to inadequate
capacity to meet timely interest and principal payments. The Fund is not
intended to be a complete investment program and there is no assurance that its
investment objective can be achieved.

Generally, the Fund will remain fully invested, and the Adviser will not attempt
to time the market. However, if a significant adverse market action is
anticipated, investment-grade debt securities may be held without limit as a
temporary defensive measure. Normally, the Fund does not purchase securities
with a view to quick turnover for capital gains. When the Fund is invested
defensively, it may not achieve its investment objective.

PORTFOLIO MANAGEMENT

The Value Discovery Fund is co-managed by Glen A. Kleczka, David S. Mitchell and
Capucine E. Price.

Glen Kleczka joined William Blair's Investment Management Services in 1996 to
lead the Fund's portfolio management team. For the previous 7 years, he was a
partner in the Private Markets and U.S. Equity groups of Brinson Partners, Inc.
and co-managed the Post-Venture Fund, whose assets totaled more than $900
million. Glen was also a member of the Private Markets Committee which approved
all venture capital and partnership investments. Previously, he spent two years
at CNA Financial Corp. as a manager of their Variable Annuity Trust equity
portfolio. While at the University of Wisconsin he was a participant at the
Center for Applied Security Analysis, a nationally recognized investment
management program. He is a member of the Investment Analyst Society of Chicago.
Education: B.S., Marquette University; M.B.A., University of Wisconsin.

David Mitchell joined William Blair in 1996 as a portfolio manager for the Fund.
In 1996, he was a partner in the U.S. Equity group of Brinson Partners, Inc. and
a member of the Post-Venture Fund management team, whose assets totaled more
than $900 million. Prior to joining Brinson, he spent four years as a co-manager
of Thomas Paine Investors, L.P., a private small-cap fund. Before joining Thomas
Paine, he was a Senior Equity Analyst on NBD's small-cap Woodward Opportunity
Fund and with Connecticut National Bank as an equity analyst and portfolio
manager. Prior to graduate studies he worked as an equity trader and a money
market portfolio manager. Education: B.A., Knox College; M.M., Northwestern
University.


Capucine "Cappy" Price joined William Blair in 1996 as a portfolio manager for
the Fund. For the previous 3 years, she was a partner in the Private Markets and
U.S. Equity groups of Brinson Partners, Inc. and a member of the Post-Venture
Fund management team, whose assets totaled more than $900 million. Previously,
she was an equity analyst for the First National Bank of Chicago. While
attending Northwestern University she was a participant in First Chicago's First
Scholar program. Education: B.A., University of Michigan; M.A., University of
Chicago; M.M., Northwestern University.



May 1, 1999, as supplemented September 30, 1999                  Prospectus   21

<PAGE>   73

INTERNATIONAL GROWTH FUND
- --------------------------------------------------------------------------------
GOAL AND STRATEGY

The International Growth Fund seeks long-term capital appreciation through
investment in well-managed, quality growth companies. Current income is not an
investment objective, although it is anticipated that capital appreciation will
normally be accompanied by modest investment income, which may vary depending on
the allocation of the investments.

INVESTMENT PROCESS

Stock Selection. In selecting companies for investment, fundamental company
analysis and stock selection are the Adviser's primary investment criteria. The
Adviser seeks companies that historically have had superior growth,
profitability and quality relative to local markets and relative to companies
within the same industry worldwide, and that are expected to continue such
performance. Such companies generally will exhibit superior business
fundamentals, including leadership in their field, quality products or services,
distinctive marketing and distribution, pricing flexibility and revenue from
products or services consumed on a steady, recurring basis. These business
characteristics should be accompanied by management that is shareholder
return-oriented and uses conservative accounting policies. Companies with
above-average returns on equity, strong balance sheets and consistent, above-
average earnings growth at reasonable valuation levels will be the primary
focus. Stock selection will take into account both local and global comparisons.


Country Allocation. In pursuing the Fund's investment objective, the Adviser
will vary the geographic diversification and types of securities based upon the
Adviser's continuous evaluation of economic, market and political trends
throughout the world. The investment of the Fund's assets in various
international securities markets tends to decrease the degree to which events in
any one country can affect the entire Fund. In making decisions regarding the
country allocation, the Adviser will consider such factors as the conditions and
growth potential of various economies and securities markets, currency exchange
rates, technological developments in the various countries and other pertinent
financial, social, national and political factors. Normally, the Fund's
investments will be spread throughout the world (excluding the United States).
The Adviser intends to maintain approximately 10 to 20 percent of the Fund's
assets in emerging markets, although that allocation will vary over time.
Emerging market companies are (i) companies organized under the laws of an
emerging market country or having securities which are traded principally on an
exchange or over-the-counter in an emerging market country; or (ii) companies
which, regardless of where organized or traded, have a significant amount of
assets (at least 50%) located in and/or derive a significant amount of their
revenues (at least 50%) from goods purchased or sold, investments made or
services performed in or with emerging market countries. Currently, emerging
markets include every country in the world other than the United States, Canada,
Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European
countries. The Adviser will seek investment opportunities in companies at
different stages of development ranging from large, well-established companies
to smaller companies at an earlier stage of development.


PORTFOLIO SECURITIES

The Fund's assets normally will be allocated among not fewer than six different
countries and will not concentrate investments in any particular industry.
However, the Fund may have more than 25% of its assets invested in any major
industrial or developed country. No more than 50% of the Fund's equity
securities may be invested in securities of issuers of any one country at any
given time.

The Fund ordinarily will invest at least 80% of its total assets in a
diversified portfolio of common stocks with above-average growth, profitability
and quality characteristics, issued by companies domiciled outside the U.S., and
in securities convertible into, exchangeable for or having the right to buy such
common stocks. For liquidity purposes, up to 20% of the Fund's assets may be
held in cash (U.S. dollars and foreign currencies) or in short-term securities,
such as repurchase agreements, and domestic and foreign money market
instruments, such as government obligations, certificates of deposit, bankers'
acceptances, time deposits, commercial paper and short-term corporate debt
securities. The Fund does not have specific rating requirements for its
short-term securities; however, the Adviser presently does not intend to invest
more than 5% of the Fund's net assets in securities rated lower than investment
grade.


 22  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   74

The Fund may enter into forward foreign currency transactions in an effort to
protect against changes in foreign exchange rates. To a limited extent, the Fund
may also invest in depository receipts, foreign currency futures, forward
foreign currency transactions, illiquid securities, investment companies,
repurchase agreements and when-issued and delayed-delivery securities, which are
described in the Investment Glossary at the end of this prospectus. The
Investment Glossary also describes the Fund's policies with regard to borrowing,
concentration, diversification, and portfolio turnover. The Fund may invest to a
very limited extent in warrants, which are described in the Statement of
Additional Information.

INVESTMENT RISKS

General. Because the Fund invests substantially all of its assets in common
stocks, the main risk is that the value of the stocks it holds may decrease in
response to the activities of an individual company or in response to general
market, business and economic conditions. If this occurs, the Fund's share price
may also decrease.

Country Allocation. The Fund seeks to invest in companies and governments of
countries having stable or improving political environments; however, there is
the possibility of expropriation or confiscatory taxation, seizure or
nationalization of foreign bank deposits or other assets, establishment of
exchange controls, the adoption of foreign government restrictions and other
adverse political, social or diplomatic developments that could affect
investments in these nations.

The risks of investing in securities of foreign issuers may include less
publicly available information, less governmental regulation and supervision of
foreign stock exchanges, brokers and issuers, a lack of uniform accounting,
auditing and financial reporting standards, practices and requirements, the
possibility of expropriation, nationalization, confiscatory taxation, adverse
changes in investment or exchange control regulations, political instability,
restrictions on the flow of international capital and difficulty in obtaining
and enforcing judgments against foreign entities. Securities of some foreign
issuers are less liquid and their prices more volatile than the securities of
U.S. companies. In addition, the time period for settlement of transactions in
foreign securities generally is longer than for domestic securities.

The securities held by the Fund will usually be denominated in currencies other
than the U.S. dollar. Therefore, changes in foreign exchange rates will affect
the value of the securities held in these Funds either beneficially or
adversely. Fluctuations in foreign currency exchange rates will also affect the
dollar value of dividends and interest earned, gains and losses realized on the
sale of securities and net investment income and gains, if any, available for
distribution to shareholders.

Operating Expenses. The Fund is expected to incur operating expenses that are
higher than those of mutual funds investing exclusively in U.S. equity
securities, since expenses such as custodial fees related to foreign investments
are usually higher than those associated with investments in U.S. securities.
Similarly, brokerage commissions on purchases and sales of foreign securities
are generally higher than on domestic securities. In addition, dividends and
interest from foreign securities may be subject to foreign withholding taxes
(see "Your Account--Taxes").


Temporary Defensive Position. Although the Fund will normally invest at least
80% of its assets in the equity securities of companies domiciled outside of the
U.S., the Fund may significantly alter its make-up as a temporary defensive
strategy. A defensive strategy would be employed only if, in the judgment of the
Adviser, investments in international equity securities became decidedly
unattractive because of current or anticipated adverse economic, financial,
political and social factors. The types of securities that might be acquired and
held for defensive purposes could include fixed-income securities and securities
issued by the U.S. or foreign governments as well as domestic or foreign money
market instruments and non-convertible preferred stock, each of which would be
of investment-grade. At such time as the Adviser determines that the Fund's
defensive strategy is no longer warranted, the Fund will adjust its portfolio
back to its normal complement of international equity securities as soon as
practicable.


Smaller Stocks. Stocks of smaller companies involve greater risk than those of
larger, more established companies. This is because smaller companies may be
dependent on a small number of products or services, may lack substantial
capital reserves and/or do not have proven track records. Smaller companies may
be more adversely affected by poor economic or market conditions, and may be
traded in low volumes, which may increase volatility and liquidity risks. The
Fund is not intended to be a complete investment program and there is no
assurance that its investment objective can be achieved.


May 1, 1999, as supplemented September 30, 1999                  Prospectus   23

<PAGE>   75

PORTFOLIO MANAGEMENT

The International Growth Fund is managed by W. George Greig.

W. George Greig, a principal of William Blair & Company, L.L.C., has managed the
Fund since 1996 when he joined the Investment Management Department as an
international portfolio manager. He headed international equities for PNC Bank
in Philadelphia from 1995 to 1996 and, prior to that, he was a founding partner
of Pilgrim Baxter & Associates, where he was an analyst, research director and
portfolio manager for over ten years. He also served as chief investment officer
of Framlington Group plc during its association with Pilgrim Baxter and founded
and managed a joint venture between the two firms. Education: B.S.,
Massachusetts Institute of Technology; M.B.A., Wharton School of the University
of Pennsylvania.


 24  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   76

EMERGING MARKETS GROWTH FUND
- --------------------------------------------------------------------------------
GOAL AND STRATEGY

The investment objective of the Emerging Markets Growth Fund is long-term
capital appreciation. The Fund pursues its objective by investing in a
diversified portfolio of equity securities issued by companies in emerging
economies worldwide.

INVESTMENT PROCESS

The Adviser seeks well-managed, high quality growth companies. Such companies
will generally exhibit superior business fundamentals, including one or more of
the following characteristics:

       REGIONAL LEADERSHIP in product quality or cost competitiveness;

       DOMINANT OR IMPROVING MARKET POSITION, generally associated with a
       competitive advantage in distribution, pricing or business franchise,
       within a growing local or regional economy; and

       SUSTAINABLE ABOVE-AVERAGE AND/OR INCREASING RETURNS on invested capital
       generated from the efficient utilization of assets, increasing profit
       margins or sound financial management, including improvements that may
       arise from the process of privatization or restructuring of corporate
       assets.

The research approach used in stock selection will focus intensively on the
soundness of corporate management, taking into account management's orientation
toward outside shareholders, incentives and ability to execute successful
strategies, commitment to transparent and conservative financial reporting
policies, and general integrity. Current income is not an investment objective,
although it is anticipated that capital appreciation will normally be
accompanied by modest investment income, which may vary depending upon the
allocation of the investments.

In pursuing the Fund's investment objective, the Adviser will vary the Fund's
geographic diversification and types of securities based upon the Adviser's
continuous evaluation of economic, market and political trends throughout the
world. The investment of the Fund's assets in various international securities
markets tends to decrease the degree to which events in any one country can
affect the entire Fund. In making decisions regarding the country allocation,
the Adviser will consider such factors as the conditions and growth potential of
various economies and securities markets, currency exchange rates, technological
developments in the various countries and other pertinent financial, social,
national and political factors. In addition, the Adviser will seek investment
opportunities in companies at different stages of development ranging from
large, well-established companies to smaller companies at an earlier stage of
development.

PORTFOLIO SECURITIES

The Fund pursues its objective by investing primarily in equity securities
issued by emerging market companies. Emerging market companies are (i) companies
organized under the laws of an emerging market country or having securities
which are traded principally on an exchange or over-the-counter in an emerging
market country; or (ii) companies which, regardless of where organized or
traded, have a significant amount of assets (at least 50%) located in and/or
derive a significant amount of their revenues (at least 50%) from goods
purchased or sold, investments made or services performed in or with emerging
market countries. Currently, emerging markets include every country in the world
other than the United States, Canada, Japan, Australia, New Zealand, Hong Kong,
Singapore and most Western European countries.

The Fund normally will allocate its investments among not less than six
different countries and will not concentrate investments in any particular
industry. No more than 50% of the Fund's equity securities will be invested in
securities of issuers in one country at any given time.

The Fund ordinarily will invest at least 65% of its total assets in equity
securities issued by emerging market companies. Equity securities include
securities convertible into, exchangeable for or having the right to buy common
stocks. For liquidity purposes, up to 35% of the Fund's assets may be held in
cash (U.S. dollars and foreign currencies) or in short-term securities, such as
repurchase agreements, and domestic and foreign money market instruments, such
as government obligations, certificates of deposit, bankers' acceptances, time
deposits, commercial paper and short-term corporate debt securities. The Fund
does not have specific rating requirements for its short-


May 1, 1999, as supplemented September 30, 1999                  Prospectus   25

<PAGE>   77

term securities; however, the Adviser presently does not intend to invest more
than 5% of the Fund's net assets in securities rated below investment grade.

The Fund may enter into forward foreign currency transactions in an effort to
protect against changes in foreign exchange rates. To a limited extent, the Fund
may also invest in depository receipts, foreign currency futures, illiquid
securities, investment companies, repurchase agreements and when-issued and
delayed delivery securities which are described in the Investment Glossary at
the end of this prospectus. The Investment Glossary also describes the Fund's
policies with regard to borrowing, concentration, diversification and portfolio
turnover. The Fund intends to invest to a very limited extent in warrants, which
are described in the Statement of Additional Information.

INVESTMENT RISKS

General. Because the Fund invests substantially all of its assets in common
stocks, the main risk is that the value of the stocks it holds may decrease in
response to the activities of an individual company or in response to general
market, business and economic conditions. If this occurs, the Fund's share price
may also decrease.

Country Allocation. The Fund seeks to invest in companies and governments of
countries having stable or improving political environments; however, there is
the possibility of expropriation or confiscatory taxation, seizure or
nationalization of foreign bank deposits or other assets, establishment of
exchange controls, the adoption of foreign government restrictions and other
adverse political, social or diplomatic developments that could affect
investments in these nations.

The risks of investing in securities of foreign issuers may include less
publicly available information, less governmental regulation and supervision of
foreign stock exchanges, brokers and issuers, a lack of uniform accounting,
auditing and financial reporting standards, practices and requirements, the
possibility of expropriation, nationalization, confiscatory taxation, adverse
changes in investment or exchange control regulations, political instability,
restrictions on the flow of international capital and difficulty in obtaining
and enforcing judgments against foreign entities. Securities of some foreign
issuers are less liquid and their prices more volatile than the securities of
U.S. companies. In addition, the time period for settlement of transactions in
foreign securities generally is longer than for domestic securities.

These risks are typically intensified in emerging markets, which are the less
developed and developing nations. Certain of these countries have in the past
failed to recognize private property rights and have at times nationalized and
expropriated the assets of private companies.

Emerging Markets. Investments in emerging markets companies are speculative and
subject to special risks. Political and economic structures in many of these
countries may be in their infancy and developing rapidly. Such countries may
also lack the social, political and economic characteristics of more developed
countries. The currencies of certain emerging market countries have experienced
a steady devaluation relative to the U.S. dollar, and continued devaluations may
adversely affect the value of a fund's assets denominated in such currencies.
Many emerging market countries have experienced substantial rates of inflation
for many years, and continued inflation may adversely affect the economies and
securities markets of such countries.

In addition, unanticipated political or social developments may affect the
values of the Fund's investments in emerging market countries and the
availability to the Fund of additional investments in these countries. The small
size, limited trading volume and relative inexperience of the securities markets
in these countries may make the Fund's investments in such countries illiquid
and more volatile than investments in more developed countries, and the Fund may
be required to establish special custodial or other arrangements before making
investments in these countries. There may be little financial or accounting
information available with respect to issuers located in these countries, and it
may be difficult as a result to assess the value or prospects of an investment
in such issuers.

In many foreign countries there is less government supervision and regulation of
business and industry practices, stock exchanges, brokers and listed companies
than in the U.S. There is an increased risk, therefore, of uninsured loss due to
lost, stolen, or counterfeit stock certificates. Prior governmental approval of
non-domestic investments may be required under certain circumstances in some
developing countries, and the extent of foreign investment in domestic companies
may be subject to limitation in other developing countries. Foreign ownership
limitations also may be imposed by the charters of individual companies in
developing countries to prevent, among other concerns,


 26  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   78

violation of foreign investment limitations. Repatriation of investment income,
capital and proceeds of sales by foreign investors may require governmental
registration and/or approval in some developing countries. The Fund could be
adversely affected by delays in or a refusal to grant any required governmental
registration or approval for such repatriation.

Further, the economies of certain developing countries may be dependent upon
international trade and, accordingly, have been and may continue to be adversely
affected by trade barriers, exchange controls, managed adjustments in relative
currency values and other protectionist measures imposed or negotiated by the
countries with which they trade. These economies also have been and may continue
to be adversely affected by economic conditions in the countries with which they
trade.

The securities held by the Fund will usually be denominated in currencies other
than the U.S. dollar. Therefore, changes in foreign exchange rates will affect
the value of the securities held in the Fund either beneficially or adversely.
Fluctuations in foreign currency exchange rates will also affect the dollar
value of dividends and interest earned, gains and losses realized on the sale of
securities and net investment income and gains, if any, available for
distribution to shareholders.

The Fund may invest in Russian securities. Russian securities involve additional
significant risks, including political and social uncertainty (for example,
regional conflicts and risk of war), currency exchange rate volatility,
pervasiveness of corruption and crime in the Russian economic, social and legal
systems, delays in settling Fund transactions and risk of loss arising out of
Russia's system of share registration and custody. Russia's system of share
registration and custody creates certain risks of loss (including the risk of
total loss) that are not normally associated with investments in other
securities markets.


Smaller Stocks. Stocks of smaller companies involve greater risk than those of
larger, more established companies. This is because smaller companies may be in
earlier stages of development, may be dependent on a small number of products or
services, may lack substantial capital reserves and/or do not have proven track
records. Smaller companies may be more adversely affected by poor economic or
market conditions, and may be traded in low volumes, which may increase
volatility and liquidity risks. From time to time, the Fund may invest in the
equity securities of very small companies, often referred to as "micro-cap"
companies. The considerations noted above are generally intensified for these
investments. Any convertible debentures issued by small companies are likely to
be lower-rated or non-rated securities, which generally involve more credit risk
than debentures in the higher rating categories and generally include some
speculative characteristics, including uncertainties or exposure to adverse
business, financial or economic conditions which could lead to inadequate
capacity to meet timely interest and principal payments.


Operating Expenses. The Fund is expected to incur operating expenses that are
higher than those of mutual funds investing exclusively in U.S. equity
securities, since expenses such as custodial fees related to foreign investments
are usually higher than those associated with investments in U.S. securities.
Similarly, brokerage commissions on purchases and sales of foreign securities
are generally higher than on domestic securities. In addition, dividends and
interest from foreign securities may be subject to foreign withholding taxes.
(For more information, see "Your Account -- Taxes.")


Temporary Defensive Position. Although the Fund will normally invest at least
65% of its assets in the equity securities of emerging market companies, the
Fund may significantly alter its make-up as a temporary defensive strategy. A
defensive strategy would be employed only if, in the judgment of the Adviser,
investments in emerging market equity securities became decidedly unattractive
because of current or anticipated adverse economic, financial, political and
social factors. The types of securities that might be acquired and held for
defensive purposes could include fixed-income securities and securities issued
by the U.S. or foreign governments as well as domestic or foreign money market
instruments and non-convertible preferred stock, each of which would be of
investment-grade. At such time as the Adviser determines that the Fund's
defensive strategy is no longer warranted, the Fund will adjust its Fund back to
its normal complement of emerging market equity securities as soon as
practicable. When the Fund is invested defensively, it may not meet its
investment objective. The Fund is not intended to be a complete investment
program, and there is no assurance that its investment objective can be
achieved.



May 1, 1999, as supplemented September 30, 1999                  Prospectus   27

<PAGE>   79

PORTFOLIO MANAGEMENT

The Emerging Markets Growth Fund is co-managed by W. George Greig and Jeffrey A.
Urbina.

W. George Greig, a principal of William Blair & Company, L.L.C., has co-managed
the Fund since its inception in 1998. He joined the Investment Management
Department in 1996 as an international portfolio manager. He headed
international equities for PNC Bank in Philadelphia from 1995 to 1996 and, prior
to that, he was a founding partner of Pilgrim Baxter & Associates, where he was
an analyst, research director and portfolio manager for over ten years. He also
served as chief investment officer of Framlington Group plc during its
association with Pilgrim Baxter and founded and managed a joint venture between
the two firms. Education: B.S., Massachusetts Institute of Technology; M.B.A.,
Wharton School of the University of Pennsylvania.

Jeffrey A. Urbina joined William Blair & Company, L.L.C. in 1996 and has
co-managed the Fund since its inception in 1998. In addition to the Emerging
Market Growth Fund, he is responsible for emerging market research for the
William Blair International Growth Fund. From 1991 to 1996, Mr. Urbina was
Senior Vice President/Director of Emerging Market Research and a Portfolio
Manager for the Van Kampen American Capital Navigator Fund, an emerging market
equity fund listed in Luxembourg. During his five years at Van Kampen American
Capital, he also served as Director of Fixed Income Research and was a member of
the Investment Policy Committee. Before joining Van Kampen American Capital, Mr.
Urbina spent ten years at Citicorp in various capacities, including as a Vice
President in the commercial real estate group in Chicago and as a commercial
lending officer in the bank's Denver office. Mr. Urbina began his banking career
at Harris Bank in Chicago, where he was an International Banking Officer.
Education: B.A., Northwestern University; M.B.A., Northwestern University
Kellogg Graduate School of Management.


 28  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   80

INCOME FUND
- --------------------------------------------------------------------------------
GOAL AND STRATEGY

The Income Fund pursues its investment objective of providing investors with as
high a level of current income as is consistent with preservation of capital by
investing primarily in a diversified portfolio of high-grade intermediate-term
debt securities.

INVESTMENT PROCESS

The Adviser seeks to outperform the total return of an index of broad
intermediate-term government and corporate high-grade debt through an actively
managed diversified portfolio of debt securities. The Adviser's investment
philosophy emphasizes shifts in the Fund's portfolio among various sectors of
the debt market, subject to the Fund's credit quality constraints for its
portfolio. The Adviser also actively manages the Fund based upon the average
duration and yield to maturity of the Fund's portfolio and the Adviser's
perceived trends in interest rates.

PORTFOLIO SECURITIES

As a matter of fundamental policy, under normal conditions at least 90% of the
Fund's assets will be invested in the following:

       U.S. DOLLAR-DENOMINATED CORPORATE DEBT SECURITIES (domestic or foreign)
       with long-term ratings of "A-" or better, or an equivalent rating, by at
       least one of the following four nationally recognized statistical rating
       organizations ("Rating Organizations"): Duff & Phelps, Inc., Fitch
       Investors Service, Inc., Moody's Investors Service, Inc. and Standard &
       Poor's Corporation;

       OBLIGATIONS OF OR GUARANTEED BY THE UNITED STATES GOVERNMENT, its
       agencies or instrumentalities. These securities include direct
       obligations of the U.S. Treasury, which differ only in their interest
       rates, maturities and time of issuance and obligations issued or
       guaranteed by U.S. Government agencies or instrumentalities, which differ
       in the degree of support provided by the U.S. Government. Although these
       securities are subject to the market risks resulting from fluctuation in
       interest rates, they will be paid in full if held to maturity;

       COLLATERALIZED OBLIGATIONS, which are debt securities issued by a
       corporation, trust or custodian, or by a U.S. Government agency or
       instrumentality, that are collateralized by a portfolio or pool of
       assets, such as mortgages, mortgage-backed securities, debit balances on
       credit card accounts or U.S. Government securities. The issuer's
       obligation to make interest and/or principal payments is secured by the
       underlying pool or portfolio of securities. The Income Fund may invest in
       collateralized obligations that are not guaranteed by a U.S. Government
       agency or instrumentality only if the collateralized obligations are
       rated A- or better, or an equivalent rating, by one of the Rating
       Organizations; and

       COMMERCIAL PAPER obligations rated within the highest grade by one of the
       four Rating Organizations.

Up to 10% of the Fund's total assets may be invested in unrated debt securities,
provided that the Adviser deems such securities to be of at least "A-" quality
and provided that the comparable debt of the issuer has a rating of at least
"A-" or its equivalent by one of the four Rating Organizations.

The anticipated dollar-weighted average maturity of the Fund is three to seven
years. The anticipated weighted average modified duration for the Fund is two to
five years, with a maximum duration on any instrument of eight years. The
Adviser will not continue to hold a security whose duration has moved above
eight years.

The duration of an instrument is different from the maturity of an instrument in
that duration measures the average period remaining until the discounted value
of the amounts due (principal and interest) under the instrument are to be paid,
rather than by the instrument's stated final maturity. For example, a portfolio
duration of five years means that if interest rates increased by one percent,
the value of the portfolio would decrease by approximately five percent.
Modified duration adjusts duration to take into account the yield to maturity
and the number of coupons received each year. For purposes of calculating
duration, instruments allowing prepayment will be assigned a maturity schedule
by the Adviser based upon industry experience.


May 1, 1999, as supplemented September 30, 1999                  Prospectus   29

<PAGE>   81

Generally the Fund will remain fully invested. However, the Fund for temporary
defensive purposes may invest up to 100% of its assets in other types of
securities, including high-quality commercial paper, obligations of banks and
savings institutions, U.S. Government securities, government agency securities
and repurchase agreements, or it may retain funds in cash. The Fund does not
invest in equity securities.

To a limited extent, the Fund may invest in illiquid securities, repurchase
agreements and when-issued and delayed delivery securities, which are described
in the Investment Glossary at the end of this prospectus. The Investment
Glossary also describes the Fund's policies with regard to borrowing,
concentration, diversification and portfolio turnover. In addition, the Fund's
policy regarding lending portfolio securities is described in the Statement of
Additional Information.

INVESTMENT RISKS

The Income Fund's investments are subject to price fluctuations resulting from
various factors, including rising or declining interest rates (interest rate
risk). The value of the portfolio's investments (other than an interest-only
class of a collateralized obligation) tends to decrease when interest rates rise
and tends to increase when interest rates fall. In addition, investments with
longer maturities, which typically provide better yields, may subject the Fund
to increased price changes resulting from market yield fluctuations.

The value of the Fund's securities is subject to the ability of the issuers of
such securities to make payment at maturity (credit risk). However, in the
opinion of the Adviser, the risk of loss of principal should be reduced due to
the relatively high quality of the investments in which the Fund primarily will
invest. Obligations that are unrated are not necessarily of lower quality than
those that are rated, but may be less marketable and, consequently, provide
higher yields. Not all securities issued or guaranteed by agencies or
instrumentalities of the U.S. Government are backed by the full faith and credit
of the United States. Such securities involve different degrees of government
backing. Some obligations issued or guaranteed by U.S. Government agencies or
instrumentalities in which the Fund may invest are backed by the full faith and
credit of the United States, such as modified pass-through certificates issued
by the Government National Mortgage Association, while others are backed
exclusively by the agency or instrumentality with limited rights of the issuer
to borrow from the U.S. Treasury (such as obligations of the Federal National
Mortgage Association and the Federal Home Loan Mortgage Corporation). Others are
backed only by the credit of the issuer itself (such as obligations of the
Student Loan Marketing Association). For a description of ratings, see Appendix
B in the Statement of Additional Information.

PORTFOLIO MANAGEMENT

The Income Fund is co-managed by Bentley Myer and James Kaplan.

Bentley Myer, a principal of William Blair & Company, L.L.C., has managed the
Fund since 1992. He joined the firm in 1991 as a fixed-income portfolio manager.
From 1983 to 1991, he was associated with LaSalle National Trust, first as head
of fixed-income investments and later as chief investment officer. Prior to
that, Bentley was head of the municipal investment section of the trust
department of Harris Trust and Savings Bank. He is currently a Trustee of Delnor
Community Hospital, as well as a member of the Investment Analysts Society of
Chicago. Education: B.A., Middlebury College; M.B.A., Wharton School of the
University of Pennsylvania.


Jim Kaplan, an associate of William Blair & Company, L.L.C., has co-managed the
Fund since 1999. He joined the firm's Investment Management Services department
in 1994 as a fixed-income portfolio manager. Prior to that, he was with First
Union National Bank for twelve years. While at First Union, Jim completed their
management training program in lending. His other responsibilities included
trading fixed-income securities such as money markets, municipal bonds and
mortgage-backed securities. Jim also assisted in the management of the bank's
portfolio. Education: B.A., Washington & Lee University.



 30  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   82

READY RESERVES FUND
- --------------------------------------------------------------------------------
GOAL AND STRATEGY

The Ready Reserves Fund pursues its investment objective of obtaining the
maximum current income consistent with preservation of capital by investing
exclusively in high-quality money market instruments. These instruments are
considered to be among the safest investments available because of their short
maturities, liquidity and high-quality ratings. The Fund seeks to maintain a net
asset value of $1.00 per share. Nevertheless, there is no guarantee that the
objective of the Fund will be achieved or that the net asset value of $1.00 per
share of the Fund will be maintained.

PORTFOLIO SECURITIES

The Fund will invest exclusively in U.S. dollar-denominated money market
instruments, including, but not limited to, those issued by:

       --      Corporations;

       --      The U.S. Government, its agencies and instrumentalities;

       --      U.S. and foreign banks;

       --      Municipalities;

       --      Foreign governments; and

       --      Multinational organizations, such as the World Bank.


The Fund has adopted certain investment policies designed to limit the market
and financial risks of the Fund. The Fund complies with the requirements of Rule
2a-7 under the Investment Company Act of 1940, which governs the maturity and
credit quality of money market funds. The Fund may invest only in securities
that, based on their short-term ratings, are deemed to be the highest grade, or
if unrated, are of equivalent quality in the judgment of the Adviser, subject to
the supervision of the Board of Directors. However, the Fund may invest up to 5%
of its total assets in securities deemed within the second highest grade, or if
unrated, are of equivalent quality. In addition, portfolio investments will be
limited to instruments that the Adviser, under the supervision of the Board of
Directors, has determined present minimal credit risks. Securities are deemed to
be highest grade if they are rated high-quality by two Rating Organizations, or,
if rated by only one Rating Organization, rated high-quality by that Rating
Organization. For example, commercial paper rated "Duff 1 minus," "Fitch 1,"
"Prime 1" and "A-1" by Duff & Phelps, Inc., Fitch Investors Service, Inc.,
Moody's Investors Service, Inc., and Standard & Poor's Corporation,
respectively, would be considered high quality. Obligations that are unrated are
not necessarily of lower quality than those that are rated, but may be less
marketable and, consequently, may provide higher yields. Further, the Fund may
invest in other corporate obligations maturing in thirteen months or less, such
as publicly traded bonds, debentures and notes, if they are rated within the two
highest grades by a Rating Organization. For a description of these ratings, see
Appendix B to the Statement of Additional Information.


To a limited extent, the Fund may invest in repurchase agreements, Section 4(2)
commercial paper, when-issued and delayed delivery securities and variable rate
securities, which are more fully described in the Investment Glossary at the end
of this prospectus. The Investment Glossary also describes the Fund's policies
with regard to borrowing, concentration and diversification.

INVESTMENT RISK

The yield paid by the Ready Reserves Fund will vary with changes in interest
rates. While the Fund seeks to maintain its $1.00 share price, there is no
guarantee that it will be able to do so.


May 1, 1999, as supplemented September 30, 1999                  Prospectus   31

<PAGE>   83

PORTFOLIO MANAGEMENT

The Ready Reserves Fund is co-managed by Bentley Myer and James Kaplan.

Bentley Myer, a principal with William Blair & Company, L.L.C., has managed the
Fund since 1992. He joined the firm in 1991 as a fixed-income portfolio manager.
From 1983 to 1991 he was associated with LaSalle National Trust, first as head
of fixed-income investments and later as chief investment officer. Prior to
that, Bentley was head of the municipal investment section of the trust
department of Harris Trust and Savings Bank. He is currently a Trustee of Delnor
Community Hospital as well as a member of the Investment Analysts Society of
Chicago. Education: B.A., Middlebury College; M.B.A., Wharton School of the
University of Pennsylvania.


Jim Kaplan, an associate of William Blair & Company, L.L.C., has co-managed the
Fund since 1999. He joined the firm's Investment Management Services department
in 1994 as a fixed-income portfolio manager. Prior to that, he was with First
Union National Bank for twelve years. While at First Union, Jim completed their
management training program in lending. His other responsibilities included
trading fixed-income securities such as money markets, municipal bonds and
mortgage-backed securities. Jim also assisted in the management of the bank's
portfolio. Education: B.A., Washington & Lee University.



 32  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   84

                            MANAGEMENT OF THE FUNDS
- --------------------------------------------------------------------------------

DIRECTORS, OFFICERS AND ADVISER. The Board of Directors of William Blair Mutual
Funds, Inc. has overall management responsibility. The duties of the directors
and officers of the Fund include supervising the business affairs of the Fund,
monitoring investment activities and practices and considering and acting upon
future plans for the Fund. The Statement of Additional Information has the names
of and additional information about the directors and officers of the Fund. The
Adviser, William Blair & Company, L.L.C., 222 West Adams Street, Chicago,
Illinois 60606, is responsible for providing investment advisory and management
services to the Funds of the Fund, subject to the direction of the Board of
Directors. The Adviser is also the principal underwriter and distributor of the
Fund and acts as agent of the Fund in the sale of its shares (the
"Distributor"). William Blair & Company, L.L.C. was founded over 60 years ago by
William McCormick Blair. Today, the firm has 150 principals and 600 employees.
The main office in Chicago houses all research and investment management
services.


The Investment Management Department oversees the assets of the six William
Blair mutual funds, along with corporate pension plans, endowments and
foundations and individual accounts. The department currently manages
approximately $12 billion in equities, fixed-income securities and cash
equivalents.

The Adviser firmly believes that clients are best served when portfolio managers
are encouraged to draw on their experience and develop new ideas. This
philosophy has helped build a hard-working, results-oriented team of over 30
portfolio managers, supported by over 40 analysts, with an exceptionally low
turnover rate. William Blair portfolio managers generally average more than ten
years with William Blair and more than two decades of experience in the
investment industry. The Adviser is registered as an investment adviser under
the Investment Advisers Act of 1940.

Each Fund pays the Adviser a monthly investment management fee. Fees paid for
each Fund's most recently completed fiscal year are shown below:

<TABLE>
<CAPTION>
FUND                             FEE AS A % OF AVERAGE NET ASSETS
- ----                             --------------------------------
<S>                              <C>
Growth Fund                                   0.75%
Value Discovery Fund                          1.15%
International Growth Fund                     1.10%
Emerging Markets Growth Fund                  1.40%
Income Fund                                   0.59%
Ready Reserves Fund                           0.59%
</TABLE>

CUSTODIAN. The Custodian is Investors Bank and Trust Company, 200 Clarendon
Street, Boston, Massachusetts 02117. State Street Bank and Trust Company, 225
Franklin Street, Boston, Massachusetts 02110, may serve as the Custodian for
Individual Retirement Accounts ("IRAs").

TRANSFER AGENT AND DIVIDEND PAYING AGENT. The Transfer Agent and Dividend Paying
Agent is State Street Bank and Trust Company, 225 Franklin Street, Boston,
Massachusetts 02110.


YEAR 2000. A critical issue has emerged in the investment services industry and
for the economy overall regarding how existing application software programs and
operating systems can accommodate the date value for the year 2000. Many
existing application software products in the marketplace were designed only to
accommodate a two-digit date position which represents the year (e.g., "95" is
stored on the system and represents the year 1995). As a result, the year 1999
(i.e., "99") could be the maximum date value these systems will be able to
accurately process. The Fund is in the process of working with the Adviser and
other service providers to assure that the Fund is prepared for the year 2000.
The Fund has been assured by the Adviser and other service providers that they
do not believe that the Fund will be materially adversely affected by year 2000.
Nevertheless, the inability of the Adviser and other service providers to
successfully address year 2000 issues could result in interruptions in the
Fund's business and have a material adverse effect on the Fund's operations.
Year 2000 problems would also increase the risks of the Fund's investments. To
assess the potential effect of the year 2000 problem, the Adviser is reviewing
information regarding the year 2000 readiness of issuers of securities the Fund
may purchase. However, this may be difficult with certain issuers. For example,
a Fund that deals with foreign service providers or invests in foreign
securities will have difficulty determining the year 2000 readiness of those
entities. This is especially true of entities



May 1, 1999, as supplemented September 30, 1999                  Prospectus   33

<PAGE>   85


or issuers in emerging markets. The financial impact of these issues for the
Fund is still being determined. There can be no assurance that potential year
2000 problems would not have a material adverse effect on the Fund.



PENDING CHANGES TO THE FUND. The Board of Directors of the Fund has approved a
proxy solicitation of shareholders of record as of             , 1999. The
matters to be considered by all shareholders include the election of Board
members, ratification of auditors and approval of a change in or elimination of
certain fundamental investment restrictions, including certain investment
objectives. In addition, the Class R shareholders will be asked to approve a
Distribution Plan under Rule 12b-1 of the Investment Company Act of 1940. The
shareholder meeting is scheduled to be held on November 30, 1999.



 34  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   86


                             CHOOSING A SHARE CLASS


- --------------------------------------------------------------------------------


CLASS A SHARES              Offered at net asset value plus a maximum sales
                            charge of 5.75% (2.00% for the Income Fund) of the
                            offering price, subject to a .25% shareholder
                            services fee. Reduced sales charges apply to
                            purchases of $50,000 or more.



CLASS B SHARES              Offered at net asset value without an initial sales
                            charge, but subject to a 0.75% Rule 12b-1
                            distribution fee, a .25% shareholder services fee
                            under Rule 12b-1 and a contingent deferred sales
                            charge that declines from 5.00% to zero on certain
                            redemptions made within seven years of purchase (for
                            the Income Fund, 2.00% to zero on certain
                            redemptions made within two years of purchase)
                            within three years of purchase. Class B shares
                            automatically convert into Class A shares (which
                            have lower ongoing expenses) eight years (three
                            years for the Income Fund) after purchase.



CLASS C SHARES              Offered at net asset value without an initial sales
                            charge, but subject to a 0.75% Rule 12b-1
                            distribution fee, a .25% shareholder services fee,
                            and a 1% contingent deferred sales charge on
                            redemptions made within one year of purchase. Class
                            C shares do not convert into another class.



CLASS I SHARES              Offered at net asset value without an initial sales
                            charge, Rule 12b-1 distribution fee or shareholder
                            services fee. Certain eligibility requirements
                            apply.



When placing purchase orders, investors must specify whether the order is for
Class A, Class B, Class C or Class I shares. Each class of shares represents
interest in the same portfolio of investments of a Fund. In addition, each Fund
offers Class R Shares through a separate prospectus.



The decision as to which class to choose depends on a number of factors,
including the amount and intended length of the investment. Investors that
qualify for reduced sales charges might consider Class A shares. Investors who
prefer not to pay an initial sales charge and who plan to hold their investment
for more than seven years might consider Class B shares. Investors who prefer
not to pay an initial sales charge but who plan to redeem their shares within
seven years might consider Class C shares. Investors who qualify for Class I
shares will not pay sales charges. For more information about the three sales
arrangements, consult your financial representative. Be aware that financial
services firms may receive different compensation depending upon which class of
shares they sell.



RULE 12b-1 PLAN



William Blair Mutual Funds have adopted a plan under Rule 12b-1 that provides
for fees payable as an expense of the Class B shares and the Class C shares that
are used by the Distributor to pay for distribution and other services provided
to shareholders of those classes. Because 12b-1 fees are paid out of Fund assets
on an ongoing basis, they will, over time, increase the cost of investment and
may cost more than other types of sales charges. Long-term shareholders of Class
B and Class C shares may pay more than the economic equivalent of the maximum
initial sales charges permitted by the National Association of Securities
Dealers, although the Distributor believes that it is unlikely, in the case of
Class B Shares, because of the automatic conversion feature of those shares.



SHAREHOLDER SERVICES AGREEMENT



Each Fund has entered into a Shareholder Services Agreement with the Distributor
that provides for fees as an expense of the Class A, B and C shares that are
used by the Distributor to pay for shareholder services provided to shareholders
of these classes.



SPECIAL FEATURES



CLASS A SHARES--COMBINED PURCHASES. Each Fund's Class A shares (or the
equivalent) may be purchased at the rate applicable to the discount bracket
attained by combining concurrent investments in Class A shares of William Blair
Mutual Funds.


May 1, 1999, as supplemented September 30, 1999                  Prospectus   35
<PAGE>   87


CLASS A SHARES--LETTER OF INTENT. The same reduced sales charges for Class A
shares also apply to the aggregate amount of purchases made by any purchaser
within a 24-month period under a written Letter of Intent ("Letter") provided by
the Distributor. The Letter, which imposes no obligation to purchase or sell
additional Class A shares, provides for a price adjustment depending upon the
actual amount purchased within such period.



CLASS A SHARES--CUMULATIVE DISCOUNT. Class A shares of a Fund may also be
purchased at the rate applicable to the discount bracket attained by adding to
the cost of shares of a Fund being purchased, the value of all Class A shares of
the above mentioned William Blair Mutual Funds (computed at the maximum offering
price at the time of the purchase for which the discount is applicable) already
owned by the investor.



CLASS A SHARES--LARGE ORDER NAV PURCHASE PRIVILEGE. Class A shares of a Fund may
be purchased at net asset value by any purchaser provided that the amount
invested in such Fund or other William Blair Mutual Funds totals at least
$1,000,000 including purchases of Class A shares pursuant to the "Combined
Purchases," "Letter of Intent" and "Cumulative Discount" features described
above (the "Large Order NAV Purchase Privilege").



EXCHANGE PRIVILEGE--GENERAL. Shareholders of Class A, Class B, Class C and Class
I shares may exchange their shares for shares of the corresponding class of a
Fund. Shares of each Class of a Fund may be exchanged for shares of Ready
Reserves Fund subject to any contingent deferred sales charge and shares of
Ready Reserves Fund may be exchanged for any class of shares of the other Funds,
subject to any applicable sales loads. Shares of a William Blair Mutual Fund
with a value in excess of $1,000,000 acquired by exchange from another William
Blair Mutual Fund, may not be exchanged thereafter until they have been owned
for 15 days (the "15 Day Hold Policy"). For purposes of determining whether the
15-day Hold Policy applies to a particular exchange, the value of the shares to
be exchanged is computed by aggregating the value of shares being exchanged for
all accounts under common control, direction or advice, including without
limitation accounts administered by a financial services firm offering market
timing, asset allocation or similar services.



For purposes of determining any contingent deferred sales charge that may be
imposed upon the redemption of the shares received on exchange, amounts
exchanged retain their original cost and purchase date.



CLASS A SHARES



PUBLIC OFFERING PRICE



Net asset value per share plus the following sales charge:



<TABLE>
<CAPTION>
                                      EQUITY FUNDS
                                      SALES CHARGE
                            ---------------------------------   DEALER REALLOWANCE
                              AS A % OF       AS A % OF NET         AS A % OF
AMOUNT OF PURCHASE          OFFERING PRICE   AMOUNT INVESTED*     OFFERING PRICE
- ------------------          --------------   ----------------   ------------------
<S>                         <C>              <C>                <C>
$0--$49,999                      5.75%             6.10%               5.00%
$50,000--$99,999                 4.50%             4.71%               3.75%
$100,000--$249,999               3.50%             3.63%               2.75%
$250,000--$499,999               2.50%             2.56%               2.00%
$500,000--$999,999               2.00%             2.04%               1.75%
$1 million and over**            0.00%             0.00%               1.00%
</TABLE>


- ---------------


*     Rounded to the nearest one hundredth percent.


**    Redemption of shares may be subject to a contingent deferred sales charge
      as discussed below.


 36  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999
<PAGE>   88


<TABLE>
<CAPTION>
                                       INCOME FUND
                                      SALES CHARGE
                            ---------------------------------   DEALER REALLOWANCE
                              AS A % OF       AS A % OF NET         AS A % OF
AMOUNT OF PURCHASE          OFFERING PRICE   AMOUNT INVESTED*     OFFERING PRICE
- ------------------          --------------   ----------------   ------------------
<S>                         <C>              <C>                <C>
$0--$49,999                      2.00%             2.04%               1.75%
$50,000--$99,999                 2.00%             2.04%               1.75%
$100,000--$249,999               1.50%             1.52%               1.25%
$250,000--$499,999               1.50%             1.52%               1.25%
$500,000--$999,999               1.00%             1.01%               0.75%
$1 million and over**            0.00%                0%               0.25%
</TABLE>


- ---------------

*     Rounded to the nearest one hundredth percent.


**    Redemption of shares may be subject to a contingent deferred sales charge
      as discussed below.



NAV PURCHASES



Class A shares of a Fund may be purchased at net asset value by:



- -    shareholders in connection with the investment or reinvestment of income
     and capital gain dividends;



- -    a participant-directed qualified retirement plan or a participant-directed
     non-qualified deferred compensation plan or a participant-directed
     qualified retirement plan which is not sponsored by a K-12 school district,
     provided in each case that such plan has not less than 200 eligible
     employees;



- -    any purchaser with investment totals in the Funds of at least $1,000,000;



- -    officers, trustees, directors, employees (including retirees) and sales
     representatives of a fund, its investment manager, its principal
     underwriter or certain affiliated companies, for themselves or members of
     their families, any trust, pension, profit-sharing or other benefit plan
     for only such persons;



- -    persons who purchase shares through bank trust departments that process
     such trades through an automated, integrated mutual fund clearing program
     provided by a third-party clearing firm;



- -    registered representatives and employees of broker-dealers having selling
     group agreements with the distributor any trust, pension, profit-sharing or
     other benefit plan for only such persons;



- -    officers, directors, and employees of service agents of the Funds;



- -    selected employees (including their spouses and dependent children) of
     banks and other financial service firms that provide services related to
     the Funds pursuant to an agreement with the Distributor;



- -    certain professionals who assist in the promotion of William Blair Mutual
     Funds pursuant to personal services contracts with the Distributor, for
     themselves or members of their families;



- -    in connection with the acquisition of the assets of or merger or
     consolidation with another investment company; and



- -    through certain investment advisers registered under the Investment
     Advisers Act of 1940 and other financial services firms, acting solely as
     agent for their clients, that adhere to certain standards established by
     the Distributor, including a requirement that such shares be purchased for
     the benefit of their clients participating in an investment advisory
     program or agency commission program under which such clients pay a fee to
     the investment advisor or other firm for portfolio management or agency
     brokerage services.



CONTINGENT DEFERRED SALES CHARGE



A contingent deferred sales charge may be imposed upon redemption of Class A
shares purchased under the Large Order NAV Purchase Privilege as follows: for
all Funds (except the Income Fund), 1% if they are redeemed within one year of
purchase and 0.50% if they are redeemed during the second year following
purchase; for the Income Fund, 0.25% if they are redeemed within one year of
purchase. The charge will not be imposed upon redemption of


May 1, 1999, as supplemented September 30, 1999                  Prospectus   37
<PAGE>   89


reinvested dividends or share appreciation. The charge is applied to the value
of the shares redeemed, excluding amounts not subject to the charge. The
contingent deferred sales charge will be waived in the event of:



- -    redemptions under a Fund's Systematic Withdrawal Plan at the maximum of 10%
     per year of the net asset value of the account;



- -    redemption of shares of a shareholder (including a registered joint owner)
     who has died;



- -    redemption of shares of a shareholder (including a registered joint owner)
     who after purchase of the shares being redeemed becomes totally disabled
     (as evidenced by a determination by the federal Social Security
     Administration);



- -    redemptions by a participant-directed qualified retirement plan or a
     participant-directed non-qualified deferred compensation plan or a
     participant-directed qualified retirement plan which is not sponsored by a
     K-12 school district;



- -    redemptions by employer sponsored employee benefit plans using the
     subaccount record keeping system made available through the Shareholder
     Service Agent or its affiliates; and



- -    redemption of shares whose dealer of record at the time of the investment
     notifies the Distributor that the dealer waives the commission applicable
     to such Large Order NAV Purchase Privilege.



DISTRIBUTION (RULE 12b-1) FEE



None



SHAREHOLDER SERVICES FEE



0.25%



EXCHANGE PRIVILEGE



Class A shares of a Fund may be exchanged for each other at their relative net
asset values.



Class A shares purchased under the Large Order NAV Purchase Privilege may be
exchanged for Class A shares of any William Blair Mutual Fund without paying any
contingent deferred sales charge. If the Class A shares received on exchange are
redeemed thereafter, a contingent deferred sales charge may be imposed.



CLASS B SHARES



PUBLIC OFFERING PRICE



Net asset value per share without any sales charge at the time of purchase.



CONTINGENT DEFERRED SALES CHARGE



A contingent deferred sales charge may be imposed upon redemption of Class B
shares. There is no such charge upon redemption of any share appreciation or
reinvested dividends. The sales charge is applied to the value of the shares
redeemed, excluding amounts not subject to the charge. The charge is computed at
the following rates applied to the value of the shares redeemed excluding
amounts not subject to the charge.



EQUITY FUNDS:



<TABLE>
<CAPTION>
     YEAR OF REDEMPTION
       AFTER PURCHASE:         FIRST   SECOND   THIRD   FOURTH   FIFTH   SIXTH   SEVENTH
       ---------------         -----   ------   -----   ------   -----   -----   -------
<S>                            <C>     <C>      <C>     <C>      <C>     <C>     <C>
Contingent Deferred
Sales Charge:                  5.00%   4.00%    3.00%   3.00%    2.00%   1.00%    0.00%
</TABLE>



 38  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   90


INCOME FUND:



<TABLE>
<CAPTION>
     YEAR OF REDEMPTION
       AFTER PURCHASE:         FIRST   SECOND   THIRD   FOURTH   FIFTH   SIXTH   SEVENTH
       ---------------         -----   ------   -----   ------   -----   -----   -------
<S>                            <C>     <C>      <C>     <C>      <C>     <C>     <C>
Contingent Deferred
Sales Charge:                  2.00%   1.00%    0.00%   0.00%    0.00%   0.00%    0.00%
</TABLE>



The contingent deferred sales charge will be waived:



- -    for redemptions to satisfy required minimum distributions after age 70 1/2
     from an IRA account (with the maximum amount subject to this waiver being
     based only upon the shareholder's William Blair IRA accounts);



- -    for redemptions made pursuant to any IRA systematic withdrawal based on the
     shareholder's life expectancy including, but not limited to, substantially
     equal periodic payments described in Code; Section 72(t)(2)(A)(iv) prior to
     age 59 1/2;



- -    for redemptions made pursuant to a systematic withdrawal plan;



- -    in the event of the total disability (as evidenced by a determination by
     the federal Social Security Administration) of the shareholder (including a
     registered joint owner) occurring after the purchase of the shares being
     redeemed; and



- -    in the event of the death of the shareholder (including a registered joint
     owner).



The contingent deferred sales charge also will be waived in connection with the
following redemptions of shares held by employer sponsored employee benefit
plans maintained on the subaccount record keeping system made available by
William Blair:



- -    redemptions to satisfy participant loan advances (note that loan repayments
     constitute new purchases for purposes of the contingent deferred sales
     charge and the conversion privilege)



- -    redemptions in connection with retirement distributions (limited at any one
     time to 10% of the total value of plan assets invested in a Fund)



- -    redemptions in connection with distributions qualifying under the hardship
provisions of the Code



- -    redemptions representing returns of excess contributions to such plans.



DISTRIBUTION (RULE 12B-1) FEE



0.75%



SHAREHOLDER SERVICES FEE



0.25%



CONVERSION FEATURE



Class B shares of a Fund will automatically convert to Class A shares of the
same Fund eight years after issuance on the basis of the relative net asset
value per share. Shares purchased through the reinvestment of dividends and
other distributions paid with respect to Class B shares in a shareholder's
account will be converted to Class A shares on a pro rata basis.



EXCHANGE PRIVILEGE



Class B shares of a Fund may be exchanged for another at their relative net
asset values without a contingent deferred sales charge.



May 1, 1999, as supplemented September 30, 1999                  Prospectus   39

<PAGE>   91


CLASS C SHARES



PUBLIC OFFERING PRICE



Net asset value per share without any sales charge at the time of purchase.



CONTINGENT DEFERRED SALES CHARGE



A contingent deferred sales charge of 1% may be imposed upon redemption of Class
C shares redeemed within one year of purchase. The charge will not be imposed
upon redemption of reinvested dividends or share appreciation. The charge is
applied to the value of the shares redeemed, excluding amounts not subject to
the charge. The contingent deferred sales charge will be waived in the event of:



- -    redemptions by a participant-directed qualified retirement plan described
     in Code Section 401(a) or a participant-directed non-qualified deferred
     compensation plan described in Code Section 457;



- -    redemptions by employer sponsored employee benefit plans (or their
     participants) using the subaccount record keeping system made available
     through the Distributor;



- -    redemption of shares of a shareholder (including a registered joint owner)
     who has died;



- -    redemption of shares of a shareholder (including a registered joint owner)
     who after purchase of the shares being redeemed becomes totally disabled
     (as evidenced by a determination by the federal Social Security
     Administration);



- -    redemptions under a Fund's systematic withdrawal plan at a maximum of 10%
     per year of the net asset value of the account;



- -    redemption of shares by an employer sponsored employee benefit plan that
     offers funds in addition to William Blair Mutual Funds and whose dealer of
     record has waived the advance of the first year administrative service and
     distribution fees applicable to such shares and agrees to receive such fees
     quarterly; and



- -    redemption of shares purchased through a dealer-sponsored asset allocation
     program maintained on an omnibus record-keeping system provided the dealer
     of record has waived the advance of the first year administrative services
     and distribution fees applicable to such shares and has agreed to receive
     such fees quarterly.



DISTRIBUTION (RULE 12b-1) FEE



0.75%



SHAREHOLDER SERVICES FEE



0.25%



CONVERSION FEATURE



None



EXCHANGE PRIVILEGE



Class C shares of a Fund may be exchanged for each other at their relative net
sales values. Class C shares may be exchanged without a contingent deferred
sales charge.



CLASS I SHARES



PUBLIC OFFERING PRICE



Net asset active without any sales change at the time of purchase.



 40  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   92


CONTINGENT DEFERRED SALES CHARGE



None



DISTRIBUTION (RULE 12b-1) FEE



None



SHAREHOLDER SERVICES FEE



None



EXCHANGE PRIVILEGE



Class I shares of a Fund may be exchanged for each other at their relative net
asset value.



ELIGIBILITY



Class I shares are available for purchase exclusively by the following
categories of institutional investors:



       (1)    clients of William Blair's Investment Management Department;



       (2)    clients of William Blair's Private Investors Department;



       (3)    tax-exempt retirement plans (Profit Sharing, 401(k), Money
              Purchase Pension and Defined Benefit Plans) of William Blair and
              it affiliates and rollover accounts from those plans;



       (4)    the following investment advisory clients of William Blair and its
              investment advisory affiliates that invest at least $1 million in
              a fund: unaffiliated benefit plans, such as qualified retirement
              plans (other than individual retirement accounts and self-directed
              retirement plans); unaffiliated banks and insurance companies
              purchasing for their own accounts; and endowment funds of
              unaffiliated non-profit organizations;



       (5)    investment-only accounts for large qualified plans, with at least
              $50 million in total plan assets or at least 1000 participants;



       (6)    trust and fiduciary accounts of trust companies and bank trust
              departments providing fee-based advisory services that invest at
              least $1 million in a Fund on behalf of each trust;



       (7)    investment companies managed by William Blair that invest
              primarily in other investment companies. Class I shares currently
              are available for purchase only from William Blair, principal
              underwriter for the Funds, and, in the case of category 6 above,
              selected dealers authorized by William Blair.



May 1, 1999, as supplemented September 30, 1999                  Prospectus   41

<PAGE>   93

                                  YOUR ACCOUNT
- --------------------------------------------------------------------------------
HOW TO BUY SHARES (By Mail, by Wire or by Telephone)


PURCHASE PRICE. All Funds (except Ready Reserves Fund) are sold at their public
offering price, which is the net asset value per share that is next computed
after receipt of your order in proper form by the Distributor, the Transfer
Agent or a designated agent thereof plus, with regard to Class A Shares of each
Fund, an initial sales charge. For the Ready Reserves Fund, the net asset value
per share normally will be $1.00. (For more information, see "Determination of
Net Asset Value.") If you fail to pay for your order, you will be liable for any
loss to the Funds and, if you are a current shareholder, the Funds may redeem
some or all of your shares to cover such loss.


NOTE: All purchases made by check should be in U.S. dollars and made payable to
William Blair Mutual Funds, Inc., or in the case of a retirement account, the
custodian or trustee of such account. Third party checks will not be accepted.
When purchases are made by check or periodic account investment, the Funds may
delay sending redemption proceeds until they determine that collected funds have
been received for the purchase of such shares, which may be up to 15 calendar
days.


RIGHT TO REJECT YOUR PURCHASE ORDER. The Fund reserves the right to decline your
purchase order upon receipt for any reason, including excessive, short-term
(market-timing) or other abusive trading practices may disrupt portfolio
management strategies and harm fund performance. To minimize harm to the Funds
and their shareholders, the Funds each reserve the right to reject any purchase
order (including exchanges) from any investor it believes has a history of
abusive trading or whose trading, in its judgment, has been or may be disruptive
to a Fund. In making this judgment, the Funds may consider trading done in
multiple accounts under common ownership or control. The Funds also reserve the
right to delay delivery of redemption proceeds--up to seven days--or to honor
certain redemptions with securities, rather than cash.


BY MAIL

OPENING AN ACCOUNT. To open a new account by mail (except for the Ready Reserves
Fund), make out a check for the amount of your investment, payable to "William
Blair Mutual Funds, Inc." Complete the account application included with this
Prospectus and mail the completed application and the check to the Transfer
Agent, State Street Bank and Trust Company ("State Street"), P.O. Box 9104,
Boston, Massachusetts 02266-9104.

For the Ready Reserves Fund, send your check and completed application to the
Distributor, William Blair Mutual Funds, Inc., 222 West Adams Street, Chicago,
Illinois 60606.

ADDING TO AN ACCOUNT. To purchase additional shares, make out a check for the
amount of your investment, payable to "William Blair Mutual Funds, Inc." Except
for the Ready Reserves Fund, mail the check, together with a letter that
specifies the portfolio name, the account number and the name(s) in which the
account is registered, to State Street Bank and Trust Company, P.O. Box 9104,
Boston, Massachusetts 02266-9104.

For the Ready Reserves Fund, send your check and letter to the Distributor,
William Blair Mutual Funds, Inc. 222 West Adams Street, Chicago, Illinois 60606.

BY WIRE

OPENING AN ACCOUNT. First, call State Street at 1-800-635-2886 (in
Massachusetts, 1-800-635-2840) for an account number. Then instruct your bank to
wire federal funds to:

       State Street Bank and Trust Co.
       ABA # 011000028
       DDA # 99029340
       Attn: Custody & Shareholder Services
       225 Franklin Street
       Boston, Massachusetts 02110

Include the portfolio name in which you are investing, your assigned account
number and the name(s) in which the account is registered. Finally, complete the
account application, indicate the account number assigned to you by State Street
and mail it to William Blair Mutual Funds, Inc., 222 West Adams Street, Chicago,
Illinois 60606.


 42  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   94

ADDING TO AN ACCOUNT. To add to your account by wire, instruct your bank to wire
federal funds to:

       State Street Bank and Trust Co.
       ABA # 011000028
       DDA # 99029340
       Attn: Custody & Shareholder Services
       225 Franklin Street
       Boston, Massachusetts 02110

In your request, specify the portfolio name in which you are investing, your
account number, and the name(s) in which the account is registered.

To add to an existing account by wire transfer of funds, you must have selected
this option on your account application.

BY TELEPHONE

OPENING AN ACCOUNT. See "By Wire."

ADDING TO AN ACCOUNT. Call State Street at 1-800-635-2886 (in Massachusetts,
1-800-635-2840). For the Ready Reserves Fund only, call your William Blair
account executive at (312) 364-8000.

Tell your account executive the portfolio name, your account number and the
name(s) in which the account is registered. You may then pay for your new shares
by mail or by wire.

To add to an existing account by telephone, you must have selected this option
on your account application.

HOW TO SELL SHARES (By Mail, by Wire or by Telephone)

You can arrange to take money out of your account by selling ("redeeming") some
or all of your shares. You may give instructions to redeem your shares by mail,
by wire or by telephone, as described below.

BY MAIL

For all Funds except the Ready Reserves Fund, to redeem shares by mail, send a
written redemption request signed by all account owners to State Street Bank and
Trust Company, P.O. Box 9104, Boston, Massachusetts 02266-9104.

For the Ready Reserves Fund, send your redemption request signed by all account
owners to the Distributor, William Blair & Company, L.L.C., 222 West Adams
Street, Chicago, Illinois 60606, to the attention of your account executive.
Amounts redeemed will be placed in your brokerage account.

FOR ALL FUNDS, WRITTEN REDEMPTION REQUESTS MUST INCLUDE:

       --      a letter that contains your name, the Fund's name and the dollar
               amount or number of shares to be redeemed;

       --      any stock certificates endorsed, or accompanied by an endorsed
               stock power, to the order of the Fund; and

       --      any other necessary documents, such as an inheritance tax consent
               or evidence of authority (for example, letters testamentary),
               dated not more than 60 days prior to receipt thereof by State
               Street or the Distributor.

BY WIRE

To redeem some or all of your shares in any Funds by wire, you may contact the
Transfer Agent, or the Distributor in the case of the Ready Reserves Fund, by
mail or telephone, as explained herein. To redeem by wire, you must have elected
this option on your account application and attached to the application a
voided, unsigned check or deposit slip for your bank account.


May 1, 1999, as supplemented September 30, 1999                  Prospectus   43

<PAGE>   95

BY TELEPHONE

TO REDEEM SHARES BY TELEPHONE, YOU MUST HAVE ELECTED THIS OPTION ON YOUR ACCOUNT
APPLICATION. For all Funds except the Ready Reserves Fund, contact the Transfer
Agent at 1-800-635-2886 (in Massachusetts, 1-800-635-2840).

For the Ready Reserves Fund, you may redeem some or all of your shares by
telephone by calling your William Blair account executive at (312) 364-8000.
Amounts redeemed will be placed in your brokerage account.

NOTE: Redemption requests should NOT be sent to the Fund or to the Distributor
(except in the case of the Ready Reserves Fund).

SIGNATURE GUARANTEES. Signature guarantees must be obtained from a bank that is
a member of the FDIC, by a brokerage firm that is a member of the NASD, or by an
eligible guarantor who is a member of, or a participant in, a signature
guarantee program. Your redemption request must include a signature guarantee if
any of the following situations apply:

       --      You wish to redeem shares having a value of $5,000 or more in a
               single transaction;

       --      Your account registration has changed; or

       --      You want a check in the amount of your redemption to be mailed to
               a different address than the one on your account application
               (address of record).

SIGNATURE GUARANTEES, IF REQUIRED, MUST APPEAR ON THE WRITTEN REDEMPTION REQUEST
AND ON ANY ENDORSED STOCK CERTIFICATE OR STOCK POWER.


REDEMPTION PRICE. The redemption price that you receive for your shares may be
more or less than the amount that you originally paid for them, depending upon
their net asset value at the time your redemption request is received in proper
order by the Distributor, the Transfer Agent or a designated agent thereof. For
the Ready Reserves Fund, the net asset value will usually be $1.00. Redemptions
may be subject to certain contingent deferred sales charges as described above.


PAYMENT FOR REDEEMED SHARES. Payment normally will be mailed to you at the
address of record for your account by the third business day after receipt by
State Street (or, in the case of the Ready Reserves Fund, the Distributor) of a
redemption request and any other required documentation and after any checks in
payment for your shares have cleared.

For the Ready Reserves Fund, if the Distributor receives notice of your request
to redeem shares by 9:30 a.m., Chicago time, the redemption will be effected as
of that date and proceeds normally will be paid that day. If notice of your
redemption request is received after that time, proceeds normally will not be
paid until the next business day.


ABUSIVE TRADING PRACTICES. Excessive, short-term (market-timing) or other
abusive trading practices may disrupt portfolio management strategies and harm
Fund performance. To minimize harm to the Funds and their shareholders, the Fund
reserve the right to reject any purchase order (including exchanges) from any
investor believed to have a history of abusive trading or chose trading, in the
Funds judgment, has been or may be disruptive to a Fund. In making this
judgment, the Funds may consider trading done in multiple accounts under common
ownership or control. The Funds also reserve the right to delay delivery of your
redemption proceeds--up to seven days--or to honor certain redemptions with
securities, rather than cash, as described in the next section. In addition,
redemption of shares from the Fund within 180 days of purchase may be subject to
a 1% redemption fee.


REDEMPTIONS IN KIND. If the Adviser determines that existing conditions make
cash payments undesirable, redemption payments may be made in whole or in part
in securities or other financial assets, valued for this purpose as they are
valued in computing the NAV for each of the Fund's shares. Shareholders
receiving securities or other financial assets on redemption may realize a gain
or loss for tax purposes, and will incur any costs of sale, as well as the
associated inconveniences. Notwithstanding the above, each of the Funds are
obligated to redeem shares solely in cash up to the lesser of $250,000 or 1% of
the net asset value of such Fund during any 90-day period for any one
shareholder of record.


 44  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   96

AUTOMATIC REDEMPTION OF SMALL ACCOUNTS. Because of the relatively high cost of
maintaining small accounts, the Fund reserves the right to redeem your shares in
any account that, following a redemption, is below a specified amount.
Currently, THE MINIMUM IS $5,000 PER ACCOUNT. Before the redemption is
processed, you will be notified that the value of your account has fallen below
the minimum and allowed to make an additional investment.

SPECIAL REDEMPTION METHODS FOR THE READY RESERVES FUND. In addition to the above
methods, shares of the Ready Reserves Fund can be redeemed by two other methods
unique to this Fund. Redemption requests will be processed after the next daily
dividend declaration at the net asset value next determined upon receipt by the
Distributor of a proper redemption request. In this way, you will receive the
net asset value of your shares and all declared but unpaid dividends on your
shares through the date of redemption.

       1.       REDEMPTION BY CHECK. To redeem shares by check, you must fill
       out the appropriate section of your account application. If your
       application for the check-writing privilege is approved, you will be
       provided with checks that may be made payable to any person IN AN AMOUNT
       NOT LESS THAN $500 NOR MORE THAN $9 MILLION. There currently is no charge
       for this service and no limit on the number of checks that you may write;
       however, these provisions are subject to change.

       The payee of the check may cash or deposit it like any other check drawn
       on a bank. When the check is presented for payment, a sufficient number
       of full and fractional shares from your account will be redeemed at their
       next-determined net asset value per share, usually $1.00, to cover the
       amount of the check. This enables you to continue earning daily dividends
       until the check clears. Canceled checks will be returned to you by State
       Street. For joint accounts, unless a single signer has been authorized on
       your account application, checks must be signed by all joint account
       owners.

       The Fund may refuse to honor checks whenever the right of redemption has
       been suspended or postponed or whenever your account is otherwise
       impaired. For instance, your account would be considered to be impaired
       when (1) there are insufficient assets to cover the check, (2) a "stop
       order" has been placed on the check, and (3) in other situations, such as
       where there is a dispute over ownership of the your account. A $25
       SERVICE FEE may be charged when a check is presented to redeem shares in
       excess of the value of your account or for an amount less than $500.

       2.       AUTOMATIC REDEMPTION. The Distributor has instituted an
       automatic redemption procedure available to Ready Reserve Fund
       shareholders who maintain certain brokerage accounts with it. The
       Distributor may use this procedure to satisfy amounts due it by you as a
       result of purchases of securities or other transactions in your brokerage
       account. Under this procedure, if you so elect, your brokerage account
       will be scanned at the opening of business each day and, after
       application of any cash balances in the brokerage account, a sufficient
       number of shares will be redeemed, effective that day at the
       next-determined net asset value, to satisfy any amounts which you are
       obligated to pay to the Distributor. You will receive all dividends
       declared but unpaid through the date of redemption.

HOW TO EXCHANGE SHARES (By Mail or by Telephone)

- --      Growth Fund
- --      Value Discovery Fund
- --      International Growth Fund
- --      Emerging Markets Growth Fund
- --      Income Fund
- --      Ready Reserves Fund


Subject to the following limitations, you may exchange shares of all Class A, B,
C and I shares into either shares of each corresponding Class A, B, C and I
shares of another Fund or into shares of the Ready Reserve Fund at their
relative net asset values so long as the shares to be acquired are available for
sale in your state of residence. There is no service fee for an exchange;
however, ONLY FOUR (4) EXCHANGES FROM A FUND ARE ALLOWED WITHIN ANY 12-MONTH
PERIOD. Exchanges will be effected by redeeming your shares and purchasing
shares of the other Fund or Funds requested.



May 1, 1999, as supplemented September 30, 1999                  Prospectus   45

<PAGE>   97

BY MAIL

You may request an exchange of your shares by writing to William Blair Mutual
Funds, Inc., Attention: Exchange Department, P.O. Box 9104, Boston,
Massachusetts 02266-9104.

BY TELEPHONE

You may also exchange your shares by telephone by completing the appropriate
section on your account application. Once your telephone authorization is on
file, State Street will honor your requests to redeem shares by telephone at
1-800-635-2886 (in Massachusetts, 1-800-635-2840). If you hold certificated
shares, you must deposit them with State Street prior to any exchange of such
shares.

Neither the Funds nor State Street will be liable for any loss, expense or cost
arising out of any telephone request pursuant to the telephone exchange
privilege, including any fraudulent or unauthorized request, and you will bear
the risk of loss, so long as the Funds or the Transfer Agent reasonably
believes, based upon reasonable verification procedures, that the telephonic
instructions are genuine. The verification procedures include (1) recording
instructions, (2) requiring certain identifying information before acting upon
instructions and (3) sending written confirmations.

DIVIDENDS AND DISTRIBUTIONS

INCOME DIVIDENDS. Each Fund earns dividends from stocks and interest from bond,
money market, and other investments, which are passed along to shareholders as
income dividends as long as expenses do not exceed income.

CAPITAL GAIN DISTRIBUTIONS. Each Fund realizes capital gains whenever it sells
securities for a higher price than it paid for them, which are passed along to
shareholders as capital gain distributions.


As a shareholder, you are entitled to your portion of the Fund's net income and
gains on its investments. Each Fund passes its earnings along to you as
distributions. The Funds' policy is to distribute substantially all net
investment income, if any, and all net realized capital gain, if any. All
distributions of income and capital gain and any return of capital have the
effect of immediately thereafter decreasing net assets value per share. Income
dividends and capital distributions will be automatically reinvested in
additional shares at net asset value on the reinvestment date, unless you
specifically request otherwise (see "Shareholder Services and Account
Policies--Dividend Options"). Cash payments are made by the Dividend Paying
Agent, State Street Bank and Trust Company, shortly following the reinvestment
date.


WHEN DIVIDENDS ARE PAID


       --      For the Growth Fund, Value Discovery Fund, International Growth
               Fund and Emerging Markets Growth Fund, all income dividends, if
               any, and capital gain distributions, if any, generally will be
               paid in December and/or January.



       --      For the Income Fund, income dividends are normally paid the
               fifteenth day of each month, if a business day, with net-realized
               long-term capital gain distributions, if any, generally being
               paid in December and/or January. The Income Fund attempts to
               maintain relatively level monthly dividends and, from time to
               time, may distribute or retain net investment income and capital
               gain or make a return of capital distribution in order to pursue
               that goal.


       --      For the Ready Reserves Fund, the Fund's net investment income
               will be declared at the close of the New York Stock Exchange on
               each day that the Fund is open for business, which is generally
               3:00 p.m., Chicago time, as a dividend to shareholders who were
               of record prior to the declaration.


The Funds may vary these dividend practices at any time. Income dividends and
any capital gain distributions on all Funds will vary from year to year.
Dividends and distributions may be subject to withholding, as required by the
Internal Revenue Service (see "Your Account--Taxes").



 46  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   98

TAXES

As with any investment, you should consider how your investment in a Fund will
be taxed. If your account is not a tax-deferred retirement account, you should
be aware of these tax implications.

TAXES ON DISTRIBUTIONS. The Fund's distributions are subject to Federal income
tax and may also be subject to state or local taxes. Distributions may be
taxable at different rates depending upon the length of time the Fund holds the
security. Your distributions are taxable when they are paid, whether you take
them in cash or reinvest them in additional shares. However, dividends declared
in October, November or December to shareholders of record as of a date in one
of those months and paid before the following February 1 are treated as having
been paid on December 31 of the calendar year declared for Federal income tax
purposes. The Funds will inform you of the amount and nature of distributions
paid.

Under the Federal tax laws, income dividends and short-term capital gains
distributions are taxed as ordinary income. Long-term capital gain distributions
are taxed as long-term capital gains. It is anticipated that a portion of the
ordinary income dividends for the Growth Fund and the Value Discovery Fund will
be eligible for the dividends-received deduction available for corporate
shareholders. The ordinary income dividends of International Growth Fund,
Emerging Markets Growth Fund, Income Fund and Ready Reserves Fund are not
eligible for the dividends-received deduction available to corporate
shareholders.

TAXES ON TRANSACTIONS. Redemptions of Fund shares and exchanges for shares of
other Funds are treated as sales and are subject to capital gains taxation. A
capital gain or loss is the difference between the price that you paid for your
shares and the price that you receive when you sell (or exchange) them. For the
Ready Reserves Fund, so long as a net asset value of $1.00 is maintained, the
sale or redemption of your shares will not result in a capital gain or loss. Any
loss recognized on the redemption of shares held six months or less will be
treated as a long-term capital loss to the extent you have received any
long-term capital gain dividends on such shares. A shareholder who redeems
shares normally will recognize a capital gain or loss for Federal income tax
purposes. If you realize a loss on the redemption of Fund shares within 30 days
before or after an acquisition of shares of the same Fund, the two transactions
may be subject to the wash sale rules of the Internal Revenue Code, resulting in
a postponement of the recognition of such loss for Federal income tax purposes.

"BUYING A DIVIDEND." If you buy shares before a Fund deducts a distribution from
its net asset value, you will pay the full price for the shares and then receive
a portion of the price back in the form of a taxable distribution. See "Your
Account--Dividends and Distributions" for payment schedules, and call the
Distributor if you have further questions.

EFFECT OF FOREIGN TAXES. Investment income received from sources within foreign
countries may be subject to foreign income taxes, which generally will reduce a
Fund's distributions. However, the United States has entered into tax treaties
with many foreign countries that entitle certain investors to a reduced rate of
tax or to certain exemptions from tax. Accordingly, the International Growth
Fund and Emerging Markets Growth Fund will operate so as to qualify for such
reduced tax rates or tax exemptions whenever practicable.

For a more detailed discussion of taxes, see the Statement of Additional
Information.


May 1, 1999, as supplemented September 30, 1999                  Prospectus   47

<PAGE>   99

                    DETERMINATION OF NET ASSET VALUE ("NAV")
- --------------------------------------------------------------------------------
WHEN AND HOW NET ASSET VALUE IS DETERMINED

The market value of a mutual fund's total assets, minus liabilities, divided by
the number of shares outstanding, is its net asset value. The value of a single
share is called its share value or share price.

The net asset value per share shall be determined as of the close of trading on
the New York Stock Exchange, which is generally 3:00 p.m., Chicago time (4:00
p.m. Eastern time), on each day when the Exchange is open. In addition, the
Ready Reserves Fund does not price its shares on the observance of Columbus Day
and Veterans Day.

When net asset value is computed, quotations of foreign securities in foreign
currencies are converted into the United States dollar equivalents at the
prevailing market rates as computed by Investors Bank & Trust Company, the
custodian. Trading in securities on exchanges and over-the-counter markets in
Europe and the Far East is normally completed at various times prior to 3:00
p.m., Chicago time, the current closing time of the New York Stock Exchange.
Trading on foreign exchanges may not take place on every day that the New York
Stock Exchange is open. Conversely, trading in various foreign markets may take
place on days when the New York Stock Exchange is not open and on other days
when net asset value is not calculated. Consequently, calculation of the net
asset value for the International Growth Fund and the Emerging Markets Growth
Fund may not occur at the same time as determination of the most current market
prices of the securities included in the calculation, and the value of the net
assets held by the International Growth Fund and the Emerging Markets Growth
Fund may be significantly affected on days when shares are not available for
purchase or redemption.

For the purposes of calculating the net asset value of the Ready Reserves Fund,
portfolio securities are valued at their amortized cost, which means their
acquisition cost adjusted for the amortization of a premium or discount.

HOW THE MARKET VALUE OF FUND SECURITIES IS DETERMINED

DOMESTIC EQUITY SECURITIES. The market value of portfolio domestic equity
securities is determined by valuing securities traded on national securities
markets at the last sale price or, in the absence of a recent sale on the date
of determination, at the latest bid price. Securities traded only on the
over-the-counter market are valued at the latest bid price.

FOREIGN EQUITY SECURITIES. The value of a foreign equity security is determined
based upon the last sale price on the foreign exchange or market on which it is
primarily traded and in the currency of that market, as of the close of the
appropriate exchange or, if there have been no sales during that day, at the
latest bid price.


FIXED-INCOME SECURITIES. Fixed-income securities are valued by using market
quotations, independent pricing services that use either prices provided by
market-makers or matrixes that produce estimates of market values obtained from
yield data relating to instruments or securities with similar characteristics.


OTHER SECURITIES AND ASSETS. Other securities, and all other assets, are valued
at a fair value as determined in good faith by, or under the direction of, the
Board of Directors.


 48  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   100

                   SHAREHOLDER SERVICES AND ACCOUNT POLICIES
- --------------------------------------------------------------------------------
The Funds provide a variety of services to help you manage your account.


AUTOMATIC SWEEP PROGRAM. You can purchase shares of the Ready Reserves Fund
through an automatic sweep program if you establish a brokerage account with the
Distributor, provided that you meet the current minimum brokerage account size
requirements. The automatic sweep program helps you to make convenient,
efficient use of free credit balances in your William Blair brokerage account.


To purchase shares of the Ready Reserves Fund through the automatic sweep
program, you must have a free credit balance in your brokerage account with the
Distributor. Currently, free credit balances are used automatically to purchase
shares. If you have a FREE CREDIT BALANCE OF AT LEAST $1,000, the Distributor
will effect on your behalf an investment in shares on an expedited basis.

       --      If you have a free credit balance resulting from securities
               transactions in your brokerage account at the opening of business
               of the Distributor, it generally will be invested in shares on
               that same day, but in no event later than the next business day.

       --      If you have a free credit balance resulting from a deposit made
               prior to 2:00 p.m., Chicago time, or a receipt of income (by
               check or wire), then it will be invested in shares no later than
               the next business day.

       --      If you have a free credit balance of at least $1 and less than
               $1,000, it will be invested in shares within a maximum of five
               business days from the day when the free credit balance is
               created.

DIVIDEND OPTIONS. You may choose to have your distributions reinvested in
additional shares automatically or paid in cash by making the appropriate
election on your account application. You may change your election at any time
by providing written notice to State Street.

       1.       AUTOMATIC DIVIDEND REINVESTMENT PLAN. The Funds automatically
reinvest all income dividends and capital gain distributions in additional
shares of stock at net asset value on the reinvestment date. (For more
information, see "Dividend and Distribution Policy.")

       2.       CASH-DIVIDEND PLAN. You may choose to have all of your income
dividends paid in cash and/or have your capital gain distributions paid in cash.
Any distributions you do not elect to have paid in cash will be reinvested
automatically in additional shares at net asset value.

       3.       AUTOMATIC DEPOSIT OF DIVIDENDS. You may elect to have all income
dividends and capital gain distributions automatically deposited in a previously
established bank account.

AUTOMATIC INVESTMENT PLAN. On your account application, you may authorize State
Street to automatically withdraw an amount of money (MINIMUM $250) from your
bank account on the fifth or twentieth day of each month. This amount will be
invested in additional shares. You may change your election at any time by
providing written notice to State Street.

SYSTEMATIC WITHDRAWAL PLAN. You may establish this plan with shares presently
held or through a new investment, which should be at least $5,000. Under this
plan, you specify a dollar amount to be paid monthly, quarterly or annually.
Shares corresponding to the specified dollar amount are automatically redeemed
from your account on the fifth business day preceding the end of the month,
quarter or year. While this plan is in effect, all income dividends and capital
gain distributions on shares in your account will be reinvested at net asset
value in additional shares. There is no charge for withdrawals, but the MINIMUM
WITHDRAWAL IS $250 PER MONTH. Depending upon the size of payments requested, and
fluctuations in the net asset value of the shares redeemed, redemptions under
this plan may reduce or even exhaust your account.

RETIREMENT PLANS. The Funds offer a variety of qualified retirement plans,
including several types of Individual Retirement Accounts ("IRAs") (e.g.
traditional IRAs, Roth IRAs and education IRAs), Simplified Employee Pension
Plans ("SEPs") and other qualified retirement plans. Additional information
concerning such plans is available from the Funds.


May 1, 1999, as supplemented September 30, 1999                  Prospectus   49

<PAGE>   101

The minimum initial retirement plan investment is $2,000 and the minimum
subsequent investment is $1,000. State Street serves as custodian for IRAs.
State Street charges a $5 plan establishment fee, an annual $15 custodial fee
and a $10 fee for each lump sum distribution from a plan. These fees may be
waived under certain circumstances.

With regard to retirement plans:
       --      participation is voluntary;
       --      you may terminate or change a plan at any time without penalty or
               charge from the Funds;
       --      the Funds will pay any additional expenses that they incur in
               connection with such plans;
       --      on your account application, you may select a plan or plans in
               which to invest;
       --      additional forms and further information may be obtained by
               writing or calling the Funds;
       --      the Funds reserve the right to change the minimum amounts for
               initial and subsequent investments or to terminate any of the
               plans;
       --      the Funds reserve the right to waive investment minimums at the
               discretion of the Distributor; and
       --      the Funds require a copy of the trust agreement when shares are
               to be held in trust.

WRITTEN CONFIRMATIONS. Each purchase, exchange or redemption transaction is
confirmed in writing to the address of record by giving details of the purchase
or redemption.

CERTIFICATED SHARES. In the interest of safekeeping and expediting transfers and
redemptions, most shareholders prefer not to receive certificates for their
shares. Rather, the value of the shares is represented by your account balance.
However, you may obtain certificated shares upon your written request. Unless
payment for shares is made by certified or cashier's check, a share certificate
will not be issued until 30 days after your purchase is completed.

USE OF INTERMEDIARIES. If you purchase or redeem shares through an investment
dealer, bank or other institution, that institution may impose charges for its
services. These charges would reduce your yield or return. You may purchase or
redeem shares directly from the Fund or with the Transfer Agent, State Street
Bank, without any such charges.

TRANSFER OF SHARES. Fund shares may be transferred by a written request
addressed to the Fund and delivered to State Street, giving the name and social
security or taxpayer identification number of the transferee and accompanied by
the same signature guarantees and documents as would be required for a
redemption, together with specimen signatures of all transferees.

SUSPENSION OF OFFERING. The Funds reserves the right to withdraw all or any part
of the offering made by this Prospectus, and the Funds or the Distributor may
reject purchase orders. From time to time, the Funds may temporarily suspend the
offering of shares to new investors. During the period of such suspension,
persons who are already shareholders of a Fund may be permitted to continue to
purchase additional shares of the Fund, to have dividends reinvested and to make
redemptions.

CONSULTATION WITH A PROFESSIONAL TAX ADVISER IS RECOMMENDED, both because of the
complexity of Federal tax laws and because various tax penalties are imposed for
excess contributions to, and late or premature distributions from, IRAs or other
qualified retirement plans. Termination of a plan shortly after its adoption may
have adverse tax consequences.

SHAREHOLDER RIGHTS. All shares of each Fund have equal rights with respect to
dividends, assets and liquidation of a Fund and equal, noncumulative voting
rights. Noncumulative voting rights allow the holder or holders of a majority of
shares, voting together for the election of directors, to elect all the
directors. All shares of each Fund will be voted in the aggregate, except when a
separate vote by Fund is required under the Investment Company Act of 1940 (the
"1940 Act"). Shares are fully paid and nonassessable when issued, are
transferable without restriction, and have no preemptive or conversion rights.
Under Maryland law, the Funds are not required to hold shareholder meetings on
an annual basis. As required by law, the Funds will, however, hold shareholder
meetings when a sufficient number of shareholders request a meeting, or as
deemed desirable by the Board of Directors, for such purposes as electing or
removing directors, changing fundamental policies or approving an investment
management agreement. (For additional information about shareholder voting
rights, see the Statement of Additional Information.)


 50  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   102

                              INVESTMENT GLOSSARY
- --------------------------------------------------------------------------------
The following glossary explains some of the types of securities in which the
Funds may invest, investment techniques they may employ, and some of the related
risks. For more information, please see the Statement of Additional Information.

BORROWING.  To a certain extent, each Fund may borrow money from banks for
limited purposes. The Growth Fund, Value Discovery Fund, International Growth
Fund and Emerging Markets Growth Fund may borrow up to 10% of their total
assets; the Income Fund and Ready Reserves Fund may borrow up to 5% of their
total assets. Most borrowing is intended only as a temporary measure for
extraordinary or emergency purposes, such as to help meet redemption requests,
and not for leverage purposes.

COLLATERALIZED OBLIGATIONS.  The Income Fund may invest in collateralized
obligations (debt securities issued by a corporation, trust or custodian or by a
U.S. Government agency or instrumentality), that are collateralized by a
portfolio or pool of assets, such as mortgages, mortgage-backed securities,
debit balances on credit card accounts or U.S. Government securities. The
issuer's obligation to make interest and/or principal payments is secured by the
underlying pool or portfolio of securities.

A variety of types of collateralized obligations are available currently, and
others may become available in the future. Some obligations are for the
guaranteed payment of only principal (the principal-only or "PO" class) or only
interest (the interest-only or "IO" class), while others are for the guaranteed
payment of both, or some variation thereof. The yields to maturity on PO and IO
class obligations are more sensitive than other obligations, with the IO class
obligations being extremely sensitive to the rate of principal payments
(including prepayments) on the related underlying assets. The Fund will invest
only in PO and IO class mortgage obligations collateralized by securities
guaranteed by the U.S. Government. Some types of collateralized obligations may
be less liquid than other types of securities. Investments in collateralized
obligations that are deemed to be illiquid, which includes PO and IO class
mortgage obligations, will be subject to the 15% limitation on illiquid assets.

The mortgage-backed collateralized obligations in which the Fund may invest
include pools of mortgage loans assembled for sale to investors by various
governmental agencies, such as the Government National Mortgage Association
("GNMA") and government-related organizations such as the Federal National
Mortgage Association ("FNMA") and the Federal Home Loan Mortgage Corporation
("FHLMC"). Payments of principal and/or interest on such mortgages, including
prepayments, are guaranteed by the agency or instrumentality. The agencies and
instrumentalities are subject to varying degrees of support by the U.S.
Government. The effective credit quality of collateralized obligations is the
credit quality of the collateral. The requirements as to collateralization are
determined by the issuer or sponsor of the collateralized obligation in order to
satisfy rating agencies. These collateralized obligations generally have excess
collateral, but typically, any guarantee is limited to a specified percentage of
the pool of assets.

The potential for appreciation in the event of a decline in interest rates may
be limited or negated by increased principal prepayments by certain
mortgage-backed securities, such as GNMA Certificates and other collateralized
obligations. During periods of declining interest rates, mortgages underlying
the security are prone to prepayment, causing the security's effective maturity
to be shortened. Prepayment


May 1, 1999, as supplemented September 30, 1999                  Prospectus   51

<PAGE>   103

of high interest rate mortgage-backed securities during times of declining
interest rates will tend to lower the return of the Fund and may even result in
losses to the Fund if the prepaid securities were acquired at a premium. Because
mortgage-backed securities tend to be sensitive to prepayment rates on the
underlying collateral, their value to the Fund is dependent upon the accuracy of
the prepayment projections used, which are a consensus derived from several
major securities dealers. The duration of many mortgage-backed securities
changes substantially in response to changes in interest rates and prepayment
rates.

CONCENTRATION.  Each of the Funds intends to invest not more than 25% of its
total asset in any one industry; however, the Ready Reserves Fund may invest
more than 25% of its total assets in the domestic banking industry. These
limitations do not apply to U.S. Government securities or government agency
securities, or to instruments, such as repurchase agreements, secured by these
instruments.

DEPOSITORY RECEIPTS.  The Growth Fund, Value Discovery Fund, International
Growth Fund and Emerging Markets Growth Fund may invest in foreign issuers
through sponsored American Depository Receipts ("ADRs"), European Depository
Receipts ("EDRs") and Global Depository Receipts ("GDRs"). Generally, an ADR is
a dollar-denominated security issued by a U.S. bank or trust company that
represents, and may be converted into, the underlying foreign security. An EDR
represents a similar securities arrangement but is issued by a European bank and
a GDR is issued by a depository. ADRs, EDRs and GDRs may be denominated in a
currency different from the underlying securities into which they may be
converted. Typically, ADRs, in registered form, are designed for issuance in
U.S. securities markets, and EDRs and GDRs, in bearer form, are designed for
issuance in European securities markets. Investments in depository receipts
entail risks similar to direct investments in foreign securities. These risks
are detailed in the sections on "Investment Risks" under the "International
Growth Fund" and "Emerging Markets Growth Fund" above and in the Statement of
Additional Information.

DIVERSIFICATION.  As a matter of fundamental policy, each Fund will not purchase
the securities of any issuer if, as a result, more than 5% of its total assets
would be invested in such issuer. For the Value Discovery Fund and Emerging
Markets Growth Fund, that limitation applies to 75% of the Fund's net assets. In
addition, each Fund will not purchase more than 10% of the outstanding voting
securities of any issuer. These limitations do not apply to U.S. Government
securities or to government agency or instrumentality securities.

FOREIGN CURRENCY FUTURES.  The International Growth Fund and Emerging Markets
Growth Fund may purchase and sell futures on foreign currencies as a hedge
against possible variation in foreign exchange rates. Foreign currency futures
contracts are traded on boards of trade and futures exchanges. A futures
contract on a foreign currency is an agreement between two parties to buy and
sell a specified amount of a particular currency for a particular price on a
future date. To the extent that the Fund engages in foreign currency futures
transactions, but fails to consummate its obligations under the contract, the
net effect to the Fund would be the same as speculating in the underlying
futures contract. Futures contracts entail certain risks. If the Adviser's
judgment about the general direction of rates or markets is wrong, the Fund's
overall performance may be less than if no such contracts had been entered into.
There may also be an imperfect correlation between movements in prices of
futures contracts and the portfolio securities being hedged. In addition, the
market prices of futures contracts may be affected by certain


 52  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   104

factors. If participants in the futures market elect to close out their
contracts through offsetting transactions rather than to meet margin
requirements, distortions in the normal relationship between the securities and
futures markets could result. In addition, because margin requirements in the
future markets are less onerous than margin requirements in the cash market,
increased participation by speculators in the futures market could cause
temporary price distortions. Due to price distortions in the futures market and
an imperfect correlation between movements in the prices of securities and
movements in the prices of futures contracts, a correct forecast of market
trends by the Fund's Adviser may still not result in a successful hedging
transaction. The Fund could also experience losses if it could not close out its
futures position because of an illiquid secondary market, and losses on futures
contracts are not limited to the amount invested in the contract. The above
circumstances could cause the Fund to lose money on the financial futures
contracts and also on the value of its portfolio securities.

To the extent required to comply with the Investment Company Act of 1940 (the
"1940 Act") and the rules and interpretations thereunder, whenever the Fund
enters into a futures contract, the Fund will maintain a segregated account
consisting of either cash or liquid securities equal to the Fund's potential
obligation under such contracts. The segregation of assets places a practical
limit on the extent to which the Fund may engage in futures contracts.

To the extent required to comply with CFTC Rule 4.5 and in order to avoid
"commodity pool operator" status, each Fund will not enter into a financial
futures contract if immediately thereafter the aggregate initial margin and
premiums for such contracts held by the Fund would exceed 5% of the liquidation
value of the Fund's assets. The Fund will not engage in transactions in
financial futures contracts for speculation, but only in an attempt to hedge
against changes in interest rates or market conditions affecting the value of
securities that the Fund holds or intends to purchase.

FORWARD FOREIGN CURRENCY TRANSACTIONS.  The International Growth Fund and
Emerging Markets Growth Fund may enter into forward foreign currency contracts
as a means of managing the risks associated with changes in exchange rates. A
forward foreign currency contract is an agreement to exchange U.S. dollars for
foreign currencies at a specified future date and specified amount which is set
by the parties at the time of entering into the contract. The Adviser will
generally use such currency contracts to fix a definite price for securities
they have agreed to buy or sell and may also use such contracts to hedge the
Fund's investments against adverse exchange rate changes. Alternatively, the
Funds may enter into a forward contract to sell a different foreign currency for
a fixed U.S. dollar amount where the Adviser believes that the U.S. dollar value
of the currency to be sold pursuant to the forward contract will fall whenever
there is a decline in the U.S. dollar value of the currency in which securities
of the Fund are denominated ("cross-hedge"). The profitability of forward
foreign currency transactions depends upon correctly predicting future changes
in exchange rates between the U.S. dollar and foreign currencies. As a result, a
Fund may incur either a gain or loss on such transactions. While forward foreign
currency transactions may help reduce losses on securities denominated in a
foreign currency, they may also reduce gains on such securities depending on the
actual changes in the currency's exchange value relative to that of the
offsetting currency involved in the transaction. The Funds will not enter into
forward foreign currency transactions for speculative purposes.

ILLIQUID SECURITIES.  The Growth Fund, Value Discovery Fund, International
Growth Fund, Emerging Markets Growth Fund and Income Fund may each invest up to
15% of their net assets in illiquid


May 1, 1999, as supplemented September 30, 1999                  Prospectus   53

<PAGE>   105

securities. The Ready Reserves Fund may invest up to 10% of its net assets in
illiquid securities. Illiquid securities are those securities that are not
readily marketable, including restricted securities and repurchase obligations
maturing in more than seven days.

INVESTMENT COMPANIES.  Subject to the provisions of the 1940 Act, the Growth
Fund, Value Discovery Fund, International Growth Fund and Emerging Markets
Growth Fund may each invest in the shares of investment companies. Investment in
other investment companies may provide advantages of diversification and
increased liquidity; however, there may be duplicative expenses, such as
advisory fees or custodial fees. Several foreign governments permit investments
by non-residents in their markets only through participation in certain
investment companies specifically organized to participate in such markets. In
addition, investments in unit trusts and country funds permit investments in
foreign markets that are smaller than those in which the Fund would ordinarily
invest directly. Investments in such pooled vehicles should enhance the
geographical diversification of the Fund's assets, while reducing the risks
associated with investing in certain smaller foreign markets. Investments in
such vehicles will provide increased liquidity and lower transaction costs than
are normally associated with direct investments in such markets; however, there
may be duplicative expenses, such as advisory fees or custodial fees.

PORTFOLIO TURNOVER RATE.  None of the Funds intend to trade portfolio securities
for the purpose of realizing short-term profits. However, each will adjust its
portfolio as considered advisable in view of prevailing or anticipated market
conditions and the Fund's investment objective, and there is no limitation on
the length of time securities must be held by the Fund prior to being sold. Fund
turnover rate will not be a limiting factor for a Fund. Although each Fund's
turnover rate will vary from year to year, it is anticipated that each Fund's
turnover rate, under normal circumstances, will be less than 100%. A higher
portfolio turnover rate would involve correspondingly higher transaction costs,
which would be borne directly by each Fund.


REAL ESTATE INVESTMENT TRUSTS.  The Value Discovery Fund may invest without
limit in real estate investment trusts ("REITs"). REITs are subject to
volatility from risks associated with investments in real estate and investments
dependent on income from real estate, such as fluctuating demand for real estate
and sensitivity to adverse economic conditions. In addition, the failure of a
REIT to continue to qualify as a REIT for tax purposes would have an adverse
effect upon the value of an investment in that REIT.


REPURCHASE AGREEMENTS.  Each Fund may invest in repurchase agreements.
Repurchase agreements are instruments under which a Fund acquires ownership of a
security, and the seller, a broker-dealer or a bank agrees to repurchase the
security at a mutually agreed upon time and price. The repurchase agreement
serves to fix the yield of the security during the Fund's holding period. The
Funds currently intend to enter into repurchase agreements only with member
banks of the Federal Reserve System or with primary dealers in U.S. Government
securities. In all cases, the Adviser, subject to the supervision of the Board
of Directors, must be satisfied with the creditworthiness of the seller before
entering into a repurchase agreement. In the event of the bankruptcy or other
default of the seller of a repurchase agreement, the Fund could incur expenses
and delays enforcing its rights under the agreement, and experience a decline in
the value of the underlying securities and loss of income. The maturity of a
security subject to repurchase may exceed one year, and, for the Income Fund,
the modified duration of a security subject to repurchase may exceed eight
years. Repurchase agreements maturing in more than seven days, together with any
securities that are restricted as to disposition under the federal securities
laws or are otherwise considered to be illiquid, will not exceed 15% of the net
assets of the Growth


 54  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
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<PAGE>   106

Fund, Value Discovery Fund, International Growth Fund, Emerging Markets Growth
Fund and Income Fund and 10% of the net assets of the Ready Reserves Fund.

SECTION 4(2) PAPER.  The Ready Reserves Fund may invest in commercial paper
issued in reliance upon the so-called "private placement" exemption from
registration afforded by Section 4(2) of the Securities Exchange Act of 1933
("Section 4(2) paper"). Section 4(2) paper is restricted as to disposition under
the Federal securities laws, and generally is sold to institutional investors
such as the Fund. Any resale by the purchaser must be in an exempt transaction.
Section 4(2) paper normally is resold to other institutional investors through
or with the assistance of the issuer or investment dealers who make a market in
the Section 4(2) paper, thus providing liquidity. The Adviser considers the
legally restricted but readily saleable Section 4(2) paper to be liquid;
however, pursuant to the procedures approved by the Fund's Board of Directors,
if a particular investment in Section 4(2) paper is not determined to be liquid,
that investment will be included within the limitation on illiquid securities.
The Adviser monitors the liquidity of each investment in Section 4(2) paper on a
continuing basis.

WHEN-ISSUED AND DELAYED DELIVERY SECURITIES.  From time to time, in the ordinary
course of business, each Fund may purchase newly issued securities appropriate
for the Fund on a "when-issued" basis, and may purchase or sell securities
appropriate for the Fund on a "delayed delivery" basis. When-issued or delayed
delivery transactions involve a commitment by the Fund to purchase or sell
particular securities, with payment and delivery to take place at a future date.
These transactions allow the Fund to lock in an attractive purchase price or
yield on a security the Fund intends to purchase. Normally, settlement occurs
within one month of the purchase or sale. During the period between purchase and
settlement, no payment is made or received by the Fund and, for delayed delivery
purchases, no interest accrues to the Fund. Because the Fund is required to set
aside cash or liquid securities at least equal in value to its commitments to
purchase when-issued or delayed delivery securities, the Adviser's ability to
manage the Fund's assets may be affected by such commitments. The Fund will only
make commitments to purchase securities on a when-issued or delayed delivery
basis with the intention of actually acquiring the securities, but it reserves
the right to sell them before the settlement date if it is deemed advisable.

VARIABLE RATE SECURITIES.  The Ready Reserves Fund may invest in instruments
having rates of interest that are adjusted periodically or that "float"
continuously or periodically according to formulae intended to minimize
fluctuation in values of the instruments ("Variable Rate Securities"). The
interest rate on a Variable Rate Security is ordinarily determined by reference
to, or is a percentage of, an objective standard such as a bank's prime rate,
the 90-day U.S. Treasury Bill rate or the rate of return on commercial paper or
bank certificates of deposit. Generally, the changes in the interest rates on
Variable Rate Securities reduce the fluctuation in the market value of such
securities. Accordingly, as interest rates decrease or increase, the potential
for capital appreciation or depreciation is less than for fixed-rate
obligations. Further, the Fund may invest in Variable Rate Securities that have
a demand feature entitling the Fund to resell the securities to the issuer or a
third party at an amount approximately equal to the principal amount thereof
plus accrued interest ("Variable Rate Demand Securities"). As is the case for
other Variable Rate Securities, the interest rate on Variable Rate Demand
Securities varies according to some objective standard intended to minimize
fluctuation in the values of the instruments. Many of these Variable Rate Demand
Securities are unrated, their transfer is restricted by the issuer, and there is
little if any secondary market for the securities. Thus, any inability of the
issuers of such securities to pay on demand could adversely affect the liquidity
of these securities. The Fund determines


May 1, 1999, as supplemented September 30, 1999                  Prospectus   55

<PAGE>   107

the maturity of Variable Rate Securities in accordance with Securities and
Exchange Commission rules, which allow the Fund to consider certain of such
instruments as having maturities shorter than the maturity date on the face of
the instrument if they are guaranteed by the U.S. Government or its agencies, if
they have a stated maturity date of one year or less, or if they have demand
features prior to maturity.


 56  William Blair Mutual Funds, Inc.     May 1, 1999, as supplemented September
30, 1999

<PAGE>   108

                              FOR MORE INFORMATION
- --------------------------------------------------------------------------------
More information about the Funds is available without charge, upon request,
including the following:

SEMI-ANNUAL/ANNUAL REPORTS

The Semi-Annual and audited Annual Reports to Shareholders include financial
statements, detailed performance information, portfolio holdings and statements
from the Fund managers. In the Fund's Annual Report, you will find a discussion
of the market conditions and investment strategies that the Adviser believes
significantly affected the Fund's performance in its last fiscal year.
Shareholder reports are incorporated by reference into this Prospectus, which
means that they are part of this Prospectus for legal purposes.

STATEMENT OF ADDITIONAL INFORMATION (SAI)

The SAI contains more detailed information about the Funds. The current SAI has
been filed with the Securities and Exchange Commission and is incorporated by
reference into this Prospectus, which means that it is part of this Prospectus
for legal purposes.

   TO OBTAIN INFORMATION:


   BY TELEPHONE

      Call: 1-800-635-2886
      (In Massachusetts 1-800-635-2840)


   BY MAIL

      Write to:
   WILLIAM BLAIR MUTUAL FUNDS, INC.
      222 West Adams Street
      Chicago, Illinois 60606
      (312) 364-8000

      or

   STATE STREET BANK AND TRUST COMPANY
      (the Fund's Transfer Agent)
      P.O. Box 9104
      Boston, MA 02266-9104

   ON THE INTERNET

     Text-only versions of fund documents can be viewed online or downloaded
     from the SEC at http://www.sec.gov

     You can also obtain copies by visiting the SEC's Public Reference Room in
     Washington, D.C. (1-800-SEC-0330) or by sending your request and a
     duplicating fee to the SEC's Public Reference Room Section, Washington,
     D.C. 20549-6009.

No person has been authorized to give any information or to make any
representations not contained in this Prospectus and, if given or made, such
information or representations must not be relied upon as having been authorized
by the Funds or their distributor. The Prospectus does not constitute an
offering by the Fund or their distributor in any jurisdiction in which such
offering may not lawfully be made.

INVESTMENT COMPANY ACT FILE NO.: 811-5344


William Blair Mutual Funds, Inc.      May 1, 1999, as supplemented September 30,
1999

<PAGE>   109
The information in this Statement of Additional Information is not complete and
may be changed. We may not sell these securities until the Registration
Statement filed with the Securities and Exchange commission is effective. This
Statement of Additional Information is not an offer to sell these securities and
is not soliciting an offer to buy these securities in any state where the offer
or sale is not permitted.

                              SUBJECT TO COMPLETION
                 PRELIMINARY STATEMENT OF ADDITIONAL INFORMATION
                              DATED AUGUST 15, 1999

                        WILLIAM BLAIR MUTUAL FUNDS, INC.
                              222 WEST ADAMS STREET
                             CHICAGO, ILLINOIS 60606
                                 (312) 364-8000

                       STATEMENT OF ADDITIONAL INFORMATION


                   MAY 1, 1999, AS SUPPLEMENTED SEPTEMBER 30,
                                     1999.



This Statement of Additional Information is not a prospectus. It should be read
in conjunction with the Prospectus of William Blair Mutual Funds, Inc. (the
"Fund") dated May 1, 1999, as supplemented September 30, 1999. The financial
statements for the William Blair Mutual Funds, Inc. for the year ended December
31, 1998, and the Report of Independent Auditors thereon are incorporated by
reference from the Annual Report to Shareholders dated December 31, 1998. The
Prospectus and Annual Report to Shareholders may be obtained without charge by
writing or calling the Fund.



                                TABLE OF CONTENTS
<TABLE>
<CAPTION>


                                                                                PAGE
                                                                                ----
<S>                                                                           <C>
MANAGEMENT.......................................................................B-1
         Investment Adviser......................................................B-1
         Distributor.............................................................B-2
         Shareholder Services....................................................B-3
         Directors and Officers..................................................B-4
         Brokerage and Fund Transactions.........................................B-8
INVESTMENT POLICIES AND RESTRICTIONS............................................B-10
         Growth Fund............................................................B-10
         Value Discovery Fund...................................................B-11
         International Growth Fund..............................................B-12
         Emerging Markets Growth Fund...........................................B-13
         Income Fund............................................................B-15
         Ready Reserves Fund....................................................B-16
INVESTMENT PRACTICES............................................................B-17
         Collateralized Obligations.............................................B-17
         Foreign Securities.....................................................B-20
         Forward Foreign Currency Transactions..................................B-23
         Foreign Currency Futures...............................................B-24
         Futures................................................................B-24
         High-Yield/High-Risk Securities........................................B-25
         Investment Companies...................................................B-25
         Illiquid Securities....................................................B-25
         Lending................................................................B-25
         Repurchase Agreements..................................................B-26
         Restricted Securities..................................................B-26
         Small Companies........................................................B-26
         Warrants...............................................................B-26
         When-Issued or Delayed Delivery Transactions...........................B-27

</TABLE>


<PAGE>   110




<TABLE>

<S>                                                                           <C>
PURCHASE, REPURCHASE AND REDEMPTION OF SHARES...................................B-27
         Initial Sales Charge Alternative -- Class A Shares.....................B-29
         Deferred Sales Charge Alternative--Class B Shares......................B-31
         Purchase of Class C Shares.............................................B-31
         Purchase of Class R and Class I Shares.................................B-31
         General................................................................B-31
         Redemptions............................................................B-33
         Special Redemptions....................................................B-33
         Contingent Deferred Sales Charge--Large Order NAV Purchase Privilege...B-33
         Contingent Deferred Sales Charge--Class B Shares.......................B-33
         Contingent Deferred Sales Charge--Class C Shares.......................B-34
         Contingent Deferred Sales Charge--General..............................B-34
         Special Features.......................................................B-35
         Class A Shares--Combined Purchases.....................................B-35
         Class A Shares--Letter of Intent.......................................B-35
         Class A Shares--Cumulative Discount....................................B-35
         Class A Shares--Availability of Quantity Discounts.....................B-35
         Exchange Privilege.....................................................B-35
GENERAL FUND INFORMATION........................................................B-36
         Determination of Net Asset Value.......................................B-36
         Performance............................................................B-37
         Historical Performance.................................................B-37
         Comparison of Fund Performance to Market Indices.......................B-40
         Tax Status.............................................................B-41
         Retirement Plans.......................................................B-42
         Independent Auditors...................................................B-43
         Legal Counsel..........................................................B-43
         Custodian..............................................................B-43
         Transfer Agent Services................................................B-43
         Reports to Shareholders................................................B-44
SHAREHOLDER RIGHTS..............................................................B-44
VALUE DISCOVERY FUND--INVESTMENT CRITERIA.......................................B-44
FUND HISTORY....................................................................B-45
FINANCIAL INFORMATION OF THE FUND...............................................B-45
APPENDIX A.......................................................................A-1
APPENDIX B.......................................................................B-1
</TABLE>


                                       ii

<PAGE>   111




                             MANAGEMENT OF THE FUND

INVESTMENT ADVISER. As stated in the Prospectus, William Blair & Company, L.L.C.
("Adviser") is the Fund's investment adviser and manager. Pursuant to an
investment advisory and management agreement, the Adviser acts as the Fund's
adviser, manages its investments, administers its business affairs, furnishes
office facilities and equipment, provides clerical, bookkeeping and
administrative services, provides shareholder and information services and
permits any of its principals or employees to serve without compensation as
directors or officers of the Fund if elected to such positions. In addition to
the management advisory fee, each portfolio pays the expenses of its operations,
including a portion of the Fund's general administrative expenses, allocated on
the basis of the portfolio's net asset value. Expenses that will be borne
directly by the portfolios include, but are not limited to, the following: the
fees and expenses of independent auditors, counsel, custodian and transfer
agent, costs of reports and notices to shareholders, stationery, printing,
postage, costs of calculating net asset value, brokerage commissions or
transaction costs, taxes, registration fees, the fees and expenses of qualifying
the Fund and its shares for distribution under Federal and state securities laws
and membership dues in the Investment Company Institute or any similar
organization.

The advisory agreement for a portfolio continues in effect from year to year for
so long as its continuation is approved at least annually (a) by a majority of
the directors who are not parties to such agreement or interested persons of any
such party except in their capacity as directors of the Fund and (b) by the
shareholders of the portfolio or the Board of Directors. The agreement may be
terminated at any time upon 60 days' notice by either party; the Fund may so
terminate the agreement either by vote of the Board of Directors or by majority
vote of the outstanding shares of the affected portfolio. The agreement may also
be terminated at any time either by vote of the Board of Directors or by
majority vote of the outstanding voting shares of the subject portfolio if the
Adviser were determined to have breached the agreement. The agreement will
terminate automatically upon assignment. The agreement provides that the Adviser
shall not be liable for any error of judgment or of law, or for any loss
suffered by the Fund in connection with the matters to which the agreement
relates, except a loss resulting from willful misfeasance, bad faith or gross
negligence on the part of the Adviser in the performance of its obligations and
duties, or by reason of its reckless disregard of its obligations and duties
under the agreement.

Upon termination of the agreement and when so requested by the Adviser, the Fund
will refrain from using the name "William Blair" in its name or in its business
in any form or combination.

For the services and facilities furnished to each portfolio, the Fund pays the
Adviser an advisory fee, which is accrued daily and paid monthly on the first
business day of the following month. The Growth Fund pays an advisory fee at a
rate of .75% of the portfolio's average daily net assets. Prior to May 1, 1996,
the Growth Fund paid an advisory fee at a rate of 0.625% of the portfolio's
average daily net assets up to $75 million and 0.50% of average daily net assets
above $75 million. For the fiscal years ended December 31, 1998, 1997 and 1996,
the Adviser received fees of $4,861,435, $4,093,417 and $3,018,755,
respectively.


The Value Discovery Fund pays an advisory fee at a rate of 1.15% of the
portfolio's average daily net assets. For services and facilities furnished to
the portfolio pursuant to the advisory agreement during the fiscal years 1998
and 1997 and for the fiscal year from December 23, 1996 (Commencement of
Operations) to December 31, 1996, the Fund paid $442,942, $241,689 and $333,
respectively.


The International Growth Fund pays an advisory fee at a rate of 1.10% of the
first $250 million of average daily net assets plus 1.00% of average daily net
assets over $250 million. Prior to May 1, 1996, the International Growth Fund
paid an advisory fee at a rate of 1.10% of the first $100,000,000 of average
daily net assets of the portfolio and .95% of average daily net assets above
$100,000,000. Under a former investment sub-advisory agreement, the Adviser paid
a sub-adviser a monthly fee at an annual rate equal to .40% of the first $100
million of average daily net assets of the portfolio and .275% of average daily
net assets above $100 million. For the services and facilities furnished during
the fiscal years ended December 31, 1998, 1997 and 1996, the Adviser received
fees of $1,557,766, $1,351,263 and $1,131,309, respectively, of which $303,364
in 1996 was paid to the former sub-adviser.

The Emerging Markets Growth Fund pays an advisory fee at a rate of 1.40% of the
portfolio's average daily net assets. The Adviser voluntarily has agreed to
reimburse the portfolio during its first year of operation should all

                                       B-1

<PAGE>   112




operating expenses, including the compensation of the Adviser but excluding
taxes, interest, extraordinary expenses and brokerage commissions or transaction
costs, exceed 2.25% of average daily net assets of the portfolio. For the
services and facilities furnished during the fiscal period from the portfolio's
incorporation on May 1, 1998 to December 31, 1998, the Adviser received fees of
$34,835. The Adviser voluntarily agreed to reimburse the portfolio during its
first year of operation should all operating expenses, including the
compensation of the Adviser but excluding taxes, interest, extraordinary
expenses and brokerage commissions or transaction costs, exceed 2.25% of average
daily net assets of the portfolio.

The Income Fund pays an advisory fee at a rate of .25% of the first $250 million
of average daily net assets plus .20% of average daily net assets over $250
million plus 5% of the gross income earned by the portfolio. Prior to May 1,
1996, the Income Fund paid an advisory fee at a rate of .25% of the first $100
million of average daily net assets of the portfolio, .20% of the next $150
million and .15% of average daily net assets in excess of $250 million, plus
5.0% of the gross income earned. For the services and facilities furnished to
the portfolio pursuant to the advisory agreement during the fiscal years ended
December 31, 1998, 1997 and 1996, the Fund paid $1,046,049, $918,833 and
$880,815, respectively.

The Ready Reserves Fund pays an advisory fee at a rate of .625% of the first
$250 million of average daily net assets, plus .60% of the next $250 million of
average daily net assets, plus .575% of the next $2 billion of average daily net
assets, plus .55% of the average daily net assets over $2.5 billion. Prior to
May 1, 1996, the Ready Reserves Fund paid an advisory fee at a rate of .625% of
the first $250 million of average daily net assets of the portfolio, .60% of the
next $250 million, .55% of the next $500 million, .50% of the next $2 billion,
 .45% of the next $2 billion and .40% of average daily net assets in excess of $5
billion. For the services and facilities furnished to the portfolio pursuant to
the advisory agreement during the fiscal years ended December 31, 1998, 1997 and
1996, the Adviser received fees of $6,215,491, $5,236,627 and $4,282,827,
respectively.

The Adviser has agreed to reimburse the Fund should all operating expenses of
the Growth Fund, Income Fund or Ready Reserves Fund, including the compensation
of the Adviser but excluding taxes, interest, extraordinary expenses and
brokerage commissions or transaction costs, exceed 1.50% of the first $30
million of average net assets of the portfolio and 1.00% of average net assets
over $30 million of the portfolio on an annual basis.


DISTRIBUTOR. Pursuant to separate Underwriting and Distribution Agreements,
William Blair & Company, L.L.C. also is the principal underwriter and
distributor ("Distributor") for shares of the Fund and acts as agent of the Fund
in the sale of its shares.



The Distribution Agreement continues in effect from year to year so long as such
continuance is approved for each class at least annually by a vote of the Board
of Directors of the Fund, including the Directors who are not interested persons
of the Fund and who have no direct or indirect financial interest in the
agreement. Each agreement automatically terminates in the event of its
assignment and may be terminated for a class at any time without penalty by a
Fund or by the Distributor upon 60 days' notice. Termination by the Fund with
respect to a class may be by vote of a majority of the Board of Directors, or a
majority of the Directors who are not interested persons of the Fund and who
have no direct or indirect financial interest in the agreement, or a "majority
of the outstanding voting securities" of the class of the Fund, as defined under
the 1940 Act. The agreement may not be amended for a class to increase the fee
to be paid by a Fund with respect to such class without approval by a majority
of the outstanding voting securities of such class of the Fund and all material
amendments must in any event be approved by the Board of Directors in the manner
described above with respect to the continuation of the agreement.



CLASS A SHARES. For its services under the Shareholder Services Agreement, the
Distributor receives a shareholder services fee from each Fund (except Ready
Reserves) under a Shareholder Service Agreement, payable monthly, at an annual
rate of 0.25% of average daily net assets of each Fund attributable to Class A
shares. The fee is accrued daily as an expense of Class A shares. The
Distributor also retains the sales charges upon the purchase of shares and pays
or allows concessions or discounts to firms for the sale of each Fund's shares.



CLASS B SHARES. For its services under the Distribution Agreement, the
Distributor receives a distribution fee from each Fund (except Ready Reserves)
under a Rule 12b-1 Plan, payable monthly, at the annual rate of 0.75% of average
daily net assets of each Fund (except Ready Reserves) attributable to Class B
shares. The Distributor also receives a shareholder service fee under a
Shareholder Service Agreement from each Fund (except Ready


                                       B-2

<PAGE>   113


Reserves), payable monthly, at an annual rate of 0.25% of average daily net
assets of each Fund (except Ready Reserves) attributed to Class B Shares. Both
fees are accrued daily as an expense of Class B shares. The Distributor also
receives any contingent deferred sales charges. See "Purchase, Repurchase and
Redemption of Shares -- Contingent Deferred Sales Charge -- Class B Shares." The
Distributor currently compensates firms for sales of Class B shares at a
commission rate of ___%.

CLASS C SHARES. For its services under the Distribution Agreement, the
Distributor receives a fee from each Fund under a Rule 12b-1 Plan, payable
monthly, at the annual rate of 0.75% of average daily net assets of each Fund
attributable to Class C shares. The Distributor also receives a shareholder
service fee under a Shareholder Service Agreement from each Fund (except Ready
Reserves), payable monthly, at an annual rate of 0.25% of average daily net
assets of each Fund (except Ready Reserves). Both fees are accrued daily as an
expense of Class C shares. [The Distributor currently advances to firms the
first year distribution fee at a rate of 0.75% of the purchase price of Class C
shares. For periods after the first year, the Distributor currently pays firms
for sales of Class C shares a distribution fee, payable quarterly, at an annual
rate of 0.75% of net assets attributable to Class C shares maintained and
serviced by the firm and the fee continues until terminated by the Distributor
or the Fund.] The Distributor also receives any contingent deferred sales
charges. See "Purchase, Repurchase and Redemption of Shares -- Contingent
Deferred Sales Charges -- Class C Shares".

CLASS R AND CLASS I SHARES. The Distributor receives no compensation from the
Funds as principal underwriter for Class R and Class I shares and pays all
expenses of distribution of each Fund's (except Ready Reserves) Class R and
Class I shares under the Distribution Agreement.

CLASS B SHARES AND CLASS C SHARES. Each Fund has adopted a plan under Rule 12b-1
that provides for fees payable as an expense of the Class B shares and Class C
shares that are used by the Distributor to pay for distribution and services for
those classes. Because 12b-1 fees are paid out of Fund assets on an ongoing
basis, they will, over time, increase the cost of an investment and cost more
than other types of sales charges.

If a Rule 12b-1 Plan (the "Plan") is terminated in accordance with its terms,
the obligation of a Fund to make payments to the Distributor pursuant to the
Plan will cease and the Fund will not be required to make any payments past the
termination date. Thus, there is no legal obligation for the Fund to pay any
expenses incurred by the Distributor in excess of its fees under a Plan, if for
any reason the Plan is terminated in accordance with its terms. Future fees
under a Plan may or may not be sufficient to reimburse the Distributor for its
expenses incurred.

SHAREHOLDER SERVICES. Shareholder services are provided to each Fund's (except
Ready Reserves) Class A, Class B and Class C shares under a Shareholder Services
Agreement with the Distributor. The Distributor bears all its expenses of
providing services pursuant to the Shareholder Services Agreement, including the
payment of shareholder service fees. The Fund pays the Distributor a shareholder
services fee, payable monthly, at an annual rate of up to 0.25% of average daily
net assets of Class A, Class B and Class C shares of the Fund.

The Distributor may enter into related arrangements with various broker-dealer
firms and other service firms ("firms"), that provide services and facilities
for their customers or clients who are shareholders of a Fund. The firms provide
such office space and equipment, telephone facilities and personnel as is
necessary or beneficial for providing information and services to their clients.
Such services and assistance may include, but are not limited to, establishing
and maintaining accounts and records, processing purchase and redemption
transactions, answering routine inquiries regarding the Fund, assistance to
clients in changing dividend and investment options, account designations and
addresses and such other services as may be agreed upon from time to time and
permitted by applicable statute, rule or regulation. For Class A, Class B and
Class C shares, the Distributor pays each firm a service fee, normally payable
quarterly, at an annual rate of up to 0.25% of the net assets in Fund accounts
that it maintains and services attributable to Class C shares commencing with
the month after investment. With respect to Class A, Class B and Class C shares,
the Distributor currently advances to firms the first-year service fee at a rate
of up to 0.25% of the purchase price of such shares. For periods after the first
year, the Distributor currently intends to pay firms a service fee at an annual
rate of up to 0.25% 0.25% and 1.00% (calculated monthly and normally paid
quarterly) of the net assets attributable to Class A, Class B and Class C
shares, respectively, maintained and serviced by the firm and the fee continues
until terminated by the Distributor or the Fund. Firms to which service fees may
be paid include broker-dealers affiliated with the Distributor.


                                       B-3

<PAGE>   114


The Distributor also may provide some of the above services and may retain any
portion of the fee under the Shareholder Services Agreement not paid to firms to
compensate itself for shareholder services performed for a Fund. Currently, the
shareholder services fee payable to the Distributor is based only upon Fund
assets in accounts for which there is a firm listed on the Fund's records and it
is intended that the Distributor will pay all the shareholder services fee rate
to be charged against all assets of a Fund while this procedure is in effect
will depend upon the proportion of Fund assets that is in accounts for which
there is a firm of record. The Board of Directors of the Fund, in its
discretion, may approve basing the fee to shareholder on all Fund assets in the
future.


Messrs. Barber, Fischer, Fuller, Greig, Hanig, Kaplan, Kayser, Kleczka,
McMullan, Myer, Sullivan and Urbina, Ms. Gassmann and Ms. Johnson, who are
directors or officers of the Fund, are also principals or employees of the
Adviser/Distributor as indicated under "Directors and Officers."

The Adviser/Distributor is a limited liability company, the affairs of which are
controlled by all its principals, none of whom owns more than 25% of the firm.
The Chief Executive Officer of the firm is E. David Coolidge, III and the
Executive Committee is comprised of Rocky Barber, E. David Coolidge, III, Edgar
D. Jannotta, John P. Kayser, Richard P. Kiphart, Albert J. Lacher, Joseph F.
LaManna, James D. McKinney and William C. Perlitz.

DIRECTORS AND OFFICERS. The directors and officers of the Fund, their ages,
their principal occupations during the last five years, their affiliations, if
any, with William Blair & Company, L.L.C. and other significant affiliations are
set forth below. Unless otherwise noted, the address of each officer and
director is 222 West Adams Street, Chicago, Illinois 60606.

CONRAD FISCHER (65),* Chairman of the Board and Director; Principal, William
Blair & Company, L.L.C.; Trustee Emeritus, Chicago Child Care Society, a
non-profit organization, and Investment Committee, Kalamazoo College.

VERNON ARMOUR (71), * (1) (2) Director; 633 East Woodland Road, Lake Forest,
Illinois 60045; private investor; Life Trustee, Illinois Institute of
Technology, Trustee, Northwestern Memorial Hospital and OTHO S.A. Sprague
Memorial Institute.

J. GRANT BEADLE (66), (1)(2) Director; 985 Riomar Drive, Vero Beach, Florida
32963; Retired Chairman and Chief Executive Officer, Union Special Corporation,
industrial sewing machine manufacturer; Retired Associate Director, Northwestern
University Institute for Learning Sciences; Oliver Products Company, Batts, Inc.
and Woodward Governor Company.

THEODORE A. BOSLER (64), (1)(2) Director; 812 Oak Street, Winnetka, Illinois
60093; Retired Principal and Vice President, Lincoln Capital Management;
Director, Thresholds, a psychiatric recovery center, and Institute of Chartered
Financial Analysts.

ANN P. MCDERMOTT (59), (1)(2) Director; 330 Willow Road, Winnetka, Illinois
60093; Trustee, Rush Presbyterian St. Luke's Medical Center; Women's Board, Rush
Presbyterian St. Luke's Medical Center; Honorary Director, Visiting Nurse
Association; Director, Presbyterian Homes; Northwestern University, Women's
Board; University of Chicago, Women's Board; Director, Washington State
University Foundation.

JAMES M. MCMULLAN (65),* Director; Principal, William Blair & Company, L.L.C.;
Director, Securities Industry Association.

JOHN B. SCHWEMM (65), (1)(2) Director; 2 Turvey Lane, Downers Grove, Illinois
60515; Retired Chairman and Chief Executive Officer, R.R. Donnelley & Sons
Company, printer; Director, USG Corp., building material product company, and
Walgreen Co., drug store chain.

ROCKY BARBER (47), Chief Executive Officer of the Fund; Principal, William Blair
& Company, L.L.C.; Vice President and Secretary, LaRabida Hospital Foundation;
Past President, Stanford Associates.

MARCO HANIG (41), President of the Fund, Associate, William Blair & Company,
L.L.C.; former Senior Vice President, First Chicago NBD; Engagement Manager,
Marakon Associates.

                                       B-4

<PAGE>   115





MARK A. FULLER, III (42), Senior Vice President; Principal, William Blair &
Company, L.L.C.

W. GEORGE GREIG (46), Senior Vice President; Principal, William Blair & Co.,
L.L.C.; former Portfolio Manager, Provident Capital Management; Manager, Akamai,
partnership affiliated with Framlington Investment Management Limited; Partner,
Pilgrim, Baxter & Greig.

GLEN KLECZKA (36), Senior Vice President; Portfolio Manager, William Blair &
Company, L.L.C.; former Partner, Brinson Partners; former Portfolio Manager, CNA
Financial Corp.

BENTLEY M. MYER (52), Senior Vice President; Principal, William Blair & Company,
L.L.C.; Director, Delnor Community Hospital.

JAMES S. KAPLAN (38), Vice President; Associate, William Blair & Company,
L.L.C.; former Vice President, First Union Bank.

JOHN P. KAYSER (49), Vice President; Principal, William Blair & Company, L.L.C.;
Director, DuPage Children's Museum.

TERENCE M. SULLIVAN (55), Vice President and Treasurer; Associate, William Blair
& Company, L.L.C.

JEFFREY A. URBINA (44), Vice President; Associate, William Blair & Company,
L.L.C.; former Director of Emerging Market Research and Portfolio Manager, Van
Kampen American Capital.

SHEILA M. JOHNSON (32), Secretary; Administrative Assistant, William Blair &
Company, L.L.C.

JANET V. GASSMANN (32), Assistant Secretary; Administrative Assistant, William
Blair & Company, L.L.C.; former Administrative Assistant, Shearson Lehman
Brothers, Inc.

- ------------------

*    Directors who are interested persons as defined in the 1940 Act.

(1)  Member of the Standing Audit Committee. (Mr. Schwemm is Chairperson of the
     Standing Audit Committee.)

(2)  Mr. Beadle, Mr. Bosler, Ms. McDermott and Mr. Schwemm employ the Adviser to
     manage assets that they control. (In addition, as a result of his former
     affiliation with the Adviser as a partner of William Blair & Company,
     L.L.C. from 1973 to 1982, Mr. Armour has a beneficial interest in a
     Deferred Profit Sharing Plan that is managed by the Adviser.)

Effective February 1, 1998, directors who are not affiliated with the Adviser
receive an annual fee of $8,000 plus $3,000 for each meeting attended in person
plus expenses, $1,500 for each meeting by telephone and $3,000 for each
committee meeting held on a different day from a board meeting. Prior to
February 1, 1998, the directors and officers not affiliated with the Adviser
received an annual fee of $4,000 plus $2,000 for each meeting attended in person
plus expenses. The directors and officers affiliated with the Adviser received
no compensation from the Fund.


                                       B-5

<PAGE>   116




The following table sets forth the compensation earned from the Fund for the
fiscal year ended December 31, 1998 by directors who are not affiliated with the
Adviser:

<TABLE>
<CAPTION>

                                                                  PENSION OR
                                                                  RETIREMENT
                                                                   BENEFITS            ESTIMATED
                                               AGGREGATE            ACCRUED              ANNUAL
                                             COMPENSATION         AS PART OF         BENEFITS UPON           TOTAL
DIRECTOR                                     FROM THE FUND       FUND EXPENSES         RETIREMENT         COMPENSATION
- --------                                     -------------       -------------       -------------        ------------
<S>                                         <C>                 <C>                  <C>                <C>
Vernon Armour............................      $20,000                   0                   0             $20,000
J. Grant Beadle..........................      $23,000                   0                   0             $23,000
Theodore A. Bosler.......................      $23,000                   0                   0             $23,000
George Kelm..............................      $18,500                   0                   0             $18,500
Ann P. McDermott.........................      $23,000                   0                   0             $23,000
John B. Schwemm..........................      $21,500                   0                   0             $21,500
</TABLE>




                                       B-6

<PAGE>   117




The following table provides certain information at June 30, 1999 with respect
to persons known to the Fund to be record holders of 5% or more of the shares of
the following portfolios:

<TABLE>
<CAPTION>

                                                    PERCENT OF FUND'S
NAME AND ADDRESS                                       OUTSTANDING
OF RECORD OWNER                                       COMMON STOCK            NUMBER OF SHARES
- ---------------                                       ------------            ----------------
<S>                                                 <C>                      <C>
GROWTH FUND
Charles Schwab & Co. Inc.                                  13.89%                 5,662,156
Attn:  Mutual Funds Dept.
101 Montgomery Street
San Francisco, CA  94104-4122

NFSC                                                       12.05%                 4,912,058
B O Our Customers
Liberty Street
One World Financial Center
Attn:  Mutual Funds Dept. 5th Fl.
New York, NY  10281

Society National Bank                                       9.35%                 3,811,449
FBO William Blair Profit Sharing Plan
P.O. Box 94870
Cleveland, OH  44101-4870

VALUE DISCOVERY FUND
William Blair & Co., L.L.C.                                 5.92%                   219,089
Ralph Gerald Portis B
222 West Adams Street
Chicago, IL  60606-5307

William Blair & Co., L.L.C.                                 5.52%                   204,261
Catlin Investment LP
222 West Adams Street
Chicago, IL  60606-5307

William Blair & Co., L.L.C.                                 5.52%                   204,261
Travis Investments LP
222 West Adams Street
Chicago, IL  60606-5307

EMERGING MARKETS GROWTH FUND
William Blair & Co., L.L.C.                                10.11%                    50,000
Edgar David Coolidge III
222 West Adams Street
Chicago, IL 60606-5307

William Blair & Co., L.L.C.                                 5.05%                    25,000
William George Greig &
222 West Adams Street
Chicago, IL 60606-5307

William Blair & Co., L.L.C.                                 5.05%                    25,000
John P. Nicholas, Trustee
222 West Adams Street
Chicago, IL 60606-5307

</TABLE>



                                       B-7

<PAGE>   118

<TABLE>
<CAPTION>

                                                    PERCENT OF FUND'S
NAME AND ADDRESS                                       OUTSTANDING
OF RECORD OWNER                                       COMMON STOCK            NUMBER OF SHARES
- ---------------                                       ------------            ----------------
<S>                                                 <C>                      <C>

INCOME FUND
Charles Schwab & Co., Inc.                                6.80%                 1,244,038
Attn:  Mutual Funds Dept.
101 Montgomery Street
San Francisco, CA  94104-4122
</TABLE>



As of June 30, the Fund's officers and directors as a group owned (or held or
shared investment or voting power with respect to) shares or % of the Growth
Fund's stock, shares or % of the Value Discovery Fund's stock, shares or % of
the International Growth Fund's stock, shares or % of the Emerging Markets
Growth Fund's stock, shares or % of the Income Fund's stock and shares or % of
the shares of the Ready Reserves Fund. These figures do not include shares of
the portfolios that may be indirectly owned by certain officers of the Fund as a
result of their interest in the William Blair Profit Sharing Plan.


BROKERAGE AND FUND TRANSACTIONS. Decisions on portfolio transactions (including
the decision to buy or sell, the appropriate price, allocation of brokerage, use
of a broker as agent or dealer as principal and negotiation of commissions)
normally are made by the Adviser. In purchasing and selling portfolio
securities, the Fund seeks to obtain the most favorable overall result, taking
into account the net price, the method of execution and research services
provided by the broker. Such research services include economic forecasts and
analytical, narrative and statistical reports on industries and companies for
consideration by the Fund and the Adviser's other clients.

Fund transactions may increase or decrease the return of a portfolio depending
upon the Adviser's ability to correctly time and execute such transactions. A
portfolio turnover rate for any year is determined by dividing the lesser of
sales or purchases (excluding in either case cash equivalents, such as
short-term corporate notes) by the portfolio's monthly average net assets and
multiplying by 100 (with all securities with maturities and expirations of one
year or less excluded from the computation). The portfolio's turnover rate will
also vary from year to year depending on market conditions. Since the Ready
Reserves Fund's assets are invested in securities with short (less than one
year) effective maturities, its portfolio will turn over many times a year. Such
securities, however, are excluded from the Securities and Exchange Commission's
required portfolio turnover rate calculations, resulting in no portfolio
turnover rate for reporting purposes.

Selection of a broker for a particular portfolio transaction depends on many
factors, some of which are subjective and which include the net price, the
confidentiality, reliability, integrity, the size and nature of the transaction
and the market in which it is to occur and any research or other services that
the broker has provided. The Adviser determines the overall reasonableness of
brokerage commissions and of premiums and discounts on principal transactions
(which do not involve commissions) by review of comparable trades for the
Adviser's other clients and in the market generally. If more than one broker is
believed to be equally qualified to effect a portfolio transaction, the Adviser
may assign the transaction to a broker that has furnished research services, but
the Adviser has no agreement, formula or policy as to allocation of brokerage.
The Fund does not ordinarily market its shares through brokers and any sales of
the Fund's shares by a broker would be neither a qualifying nor disqualifying
factor in allocating brokerage. All the Fund's 1998 portfolio transactions were
with brokers that met the above requirements, some of which provided research or
other services to the Adviser.

The Fund may pay to brokers that provide research services to the Adviser a
commission higher than another broker might have charged if it is determined
that the commission is reasonable in relation to the value of the brokerage and
research services that are provided, viewed in terms of either the particular
transaction or the Adviser's overall responsibility to its advisory accounts.
The extent to which such commissions exceed commissions solely for execution
cannot be determined, but such research services, which are involved in
portfolio transactions for the Fund and for the Adviser's other advisory
accounts, can be of benefit to both the Fund and such other accounts. The value
of research services that are provided by brokers who handle portfolio
transactions for the Fund cannot be precisely determined and such services are
supplemental to the Adviser's own efforts, which are undiminished


                                      B-8

<PAGE>   119

thereby. The Adviser does not believe that its expenses are reduced by reason of
such services, which benefit the Fund and the Adviser's other clients.
Transactions in over-the-counter securities are generally executed as principal
trades with primary market makers, except where it is believed that a better
combination of price and execution could otherwise be obtained. The Adviser
receives research products and services from broker/dealers and third parties in
the form of written reports on individual companies and industries of particular
interest to the Adviser, general economic conditions, pertinent Federal and
State legislative developments and changes in accounting practices; direct
access by telephone or meetings with leading research analysts throughout the
financial community, corporate management personnel, and industry experts,
comparative performance and evaluation and technical measurement services for
issuers, industries and the market as a whole; access to and monitoring of
equity valuation models; and services from recognized experts on investment
matters of particular interest to the Adviser.

The Growth Fund paid total brokerage fees of $515,832, $422,714 and $394,561 in
1998, 1997 and 1996, respectively. None of these brokerage fees were paid to a
broker that was an affiliated person of the Fund or to a broker of which an
affiliated person was an affiliated person of the Fund or of the Adviser. The
increase in brokerage fees from year to year is in proportion to the change in
the Fund's asset size.

The Value Discovery Fund paid total brokerage fees of $103,906 in 1998, $35,216
in 1997 and $12 for the period from December 23, 1996 (Commencement of
Operations) to December 31, 1996. None of these brokerage fees were paid to a
broker that was an affiliated person of the Fund or to a broker of which an
affiliated person was an affiliated person of the Fund or of the Adviser.

The International Growth Fund paid brokerage fees of $889,064, $820,267 and
$779,507 in 1998, 1997 and 1996, respectively. None of these brokerage fees were
paid to a broker that was an affiliated person of the Fund or to a broker of
which an affiliated person was an affiliated person of the Fund or of the
Adviser.

The Emerging Markets Growth Fund paid brokerage fees of $60,161 in 1998. None of
these brokerage fees were paid to a broker that was an affiliated person of the
Fund or to a broker of which an affiliated person was an affiliated person of
the Fund or the Adviser.

Purchases and sales of portfolio securities for the Income Fund and the Ready
Reserves Fund usually are principal transactions, either directly with the
issuer or with an underwriter or market maker, with no brokerage commissions
paid by the portfolio. No brokerage commissions were paid by the Income Fund or
the Ready Reserves Fund during the fiscal years ended December 31, 1998, 1997
and 1996. Purchases from underwriters will include a commission or concession
paid by the issuer to the underwriter and purchases from dealers serving as
market makers will include the spread between the bid and asked prices. The
primary consideration in the allocation of transactions is prompt execution of
orders in an effective manner at the most favorable price.

The investment decisions for the Fund are reached independently from those for
other accounts managed by the Adviser. Such other accounts also may make
investments in the same type of instruments or securities as the Fund at the
same time as the Fund. In those instances where the Fund and another client of
the Adviser trade in the same type of instrument at the same time, the Adviser
has established allocation procedures under its Code of Ethics that ensures an
equitable allocation of such trades among its various clients and the Fund. In
some cases this procedure may affect the size or price of the position
obtainable for the Fund. However, it is the opinion of the Board of Directors
that the benefits available because of the Adviser's organization outweigh any
disadvantages that may arise from exposure to simultaneous transactions.

No portfolio transactions are executed for the Fund with or through the Adviser
or any affiliated broker-dealer of the Adviser. The Fund may purchase securities
from other members of an underwriting syndicate of which the Adviser or
an affiliated broker-dealer is a participant, but only under conditions set
forth in applicable rules of the Securities and Exchange Commission and in
accordance with procedures adopted and reviewed periodically by the Board of
Directors.


                                       B-9

<PAGE>   120





                      INVESTMENT POLICIES AND RESTRICTIONS

The Fund has adopted certain fundamental investment restrictions for each
portfolio that, along with the portfolio's investment objective, can not be
changed without approval by holders of a "majority of the outstanding voting
securities" of the portfolio, which is defined in the Investment Company Act of
1940 (the "1940 Act") to mean the lesser of (a) 67% of the shares of the
portfolio at a meeting where more than 50% of the outstanding voting shares of
the portfolio are present in person or by proxy; or (b) more than 50% of the
outstanding voting shares of the portfolio. All percentage restrictions on
investments apply at the time the investment is made and shall not be considered
to violate the limitations unless, immediately after or as a result of the
investment, a violation of the restriction occurs. There can be no assurance
that a portfolio will meet its investment objective.

GROWTH FUND.

(1)  The portfolio will operate as an open-end, diversified, management type
     investment company, as defined in the 1940 Act.

The Growth Fund may not:

(2)  Invest in any enterprise for the purpose of exercising control or
     management thereof.

(3)  Buy or sell real estate or real estate loans.

(4)  Underwrite the securities of other issuers.

(5)  Make loans to other persons.

(6)  Purchase or sell commodities or commodity contracts.

(7)  Issue senior securities.

(8)  Borrow money, except from banks for current obligations of a minor
     character incurred in the ordinary course of business, nor borrow amounts
     in excess of 10% of its gross assets. (The portfolio does not presently
     intend to borrow any amount in excess of 5% of its gross assets.)

(9)  Make an investment if doing so would cause more than 25% of its total
     assets to be invested in any one industry.

The following are the portfolio's non-fundamental operating policies, which may
be changed by the Fund's Board of Directors without shareholder approval.

The Growth Fund may not:

(10) Pledge, or create a lien on, its assets.

(11) Purchase any security if doing so would cause more than 10% of the voting
     securities of the issuer to be held by the portfolio.

(12) Purchase, except for securities acquired as part of a merger, consolidation
     or acquisition of assets, more than 3% of the stock of another investment
     company, except as otherwise permitted by statute, rule, exemptive order,
     SEC no-action letter or investment restriction.

(13) Invest in futures contracts, puts, calls, straddles, spreads or any
     combination thereof.

(14) Invest in illiquid securities if, as a result of such investment, more than
     15% of its net assets would be invested in illiquid securities.

                                      B-10

<PAGE>   121

(15) Sell securities short, unless the portfolio owns or has the right to obtain
     securities equivalent in kind and amount to the securities sold short, or
     unless it covers such short sale as required by the current rules and
     positions of the Securities and Exchange Commission or its staff and
     provided that transactions in futures contracts or other derivative
     instruments are not deemed to constitute selling securities short.

(16) Purchase securities on margin, except that the Fund may obtain such
     short-term credits as are necessary for the clearance of transactions; and
     provided that margin deposits in connection with futures contracts or other
     derivative instruments shall not constitute purchasing securities on
     margin.

VALUE DISCOVERY FUND.

The Value Discovery Fund:

(1)  May not with respect to 75% of its total assets, purchase the securities of
     any issuer (except securities issued or guaranteed by the U.S. government
     or its agencies or instrumentalities) if, as a result, (i) more than 5% of
     the portfolio's total assets would be invested in the securities of that
     issuer or (ii) the portfolio would hold more than 10% of the outstanding
     voting securities of that issuer.

(2)  May (i) borrow money from banks and (ii) make other investments or engage
     in other transactions permissible under the 1940 Act which may involve a
     borrowing, provided that the combination of (i) and (ii) shall not exceed
     331/3% of the value of the portfolio's total assets (including the amount
     borrowed), less the portfolio's liabilities (other than borrowings), or
     such other percentage permitted by law, except that the portfolio may
     borrow up to an additional 5% of its total assets (not including the amount
     borrowed) from a bank for temporary or emergency purposes (but not for
     leverage or the purchase of investments).

Note: Presently, the Value Discovery Fund only intends to borrow from banks for
temporary or emergency purposes. However, the portfolio may borrow money from
banks and make other investments or engage in other transactions permissible
under the 1940 Act which may be considered a borrowing (such as mortgage dollar
rolls and reverse repurchase agreements).

(3)  May not issue senior securities, except as permitted under the 1940 Act.

(4)  May not act as an underwriter of another issuer's securities, except to the
     extent that the portfolio may be deemed to be an underwriter within the
     meaning of the Securities Act of 1933 in connection with the purchase and
     sale of portfolio securities.

(5)  May not purchase or sell physical commodities unless acquired as a result
     of ownership of securities or other instruments (but this shall not prevent
     the portfolio from purchasing or selling options, futures contracts, or
     other derivative instruments or from investing in securities or other
     instruments backed by physical commodities).


(6)  May not make loans if, as a result, more than 33 1/3% of the portfolio's
     total assets would be lent to other persons, except through (i) purchases
     of debt securities or other debt instruments or (ii) engaging in repurchase
     agreements.


(7)  May not purchase the securities of any issuer if, as a result, 25% or more
     of the portfolio's total assets would be invested in the securities of
     issuers, the principal business activities of which are in the same
     industry.

(8)  May not purchase or sell real estate unless acquired as a result of
     ownership of securities or other instruments (but this shall not prohibit
     the portfolio from purchasing or selling securities or other instruments
     backed by real estate or of issuers engaged in real estate activities).

The following are the portfolio's non-fundamental operating policies, which may
be changed by the Fund's Board of Directors without shareholder approval.

                                      B-11

<PAGE>   122

The Value Discovery Fund may not:

(9)  Sell securities short, unless the portfolio owns or has the right to obtain
     securities equivalent in kind and amount to the securities sold short, or
     unless it covers such short sale as required by the current rules and
     positions of the Securities and Exchange Commission or its staff and
     provided that transactions in futures contracts or other derivative
     instruments are not deemed to constitute selling securities short.

(10) Purchase securities on margin, except that the Fund may obtain such
     short-term credits as are necessary for the clearance of transactions; and
     provided that margin deposits in connection with futures contracts or other
     derivative instruments shall not constitute purchasing securities on
     margin.

(11) Invest in illiquid securities if, as a result of such investment, more than
     15% of its net assets would be invested in illiquid securities.

(12) Purchase, except for securities acquired as part of a merger, consolidation
     or acquisition of assets, more than 3% of the stock of another investment
     company, except as otherwise permitted by statute, rule, exemptive order,
     SEC no-action letter or investment restriction.

(13) Engage in futures transactions which are impermissible pursuant to Rule 4.5
     under the Commodity Exchange Act and, in accordance with Rule 4.5, will use
     futures transactions solely for bona fide hedging transactions (within the
     meaning of the Commodity Exchange Act); provided, however, that the
     portfolio may, in addition to bona fide hedging transactions, use futures
     transactions if the aggregate initial margin and premiums required to
     establish such positions do not exceed 5% of the portfolio's net assets. In
     addition, the aggregate margin deposits required on all futures
     transactions being held will not exceed 5% of the portfolio's total assets.

(14) Pledge, mortgage or hypothecate any assets owned by the portfolio except as
     may be necessary in connection with permissible borrowings or investments
     and then such pledging, mortgaging or hypothecating may not exceed 331/3%
     of the portfolio's total assets at the time of the borrowing or investment.

INTERNATIONAL GROWTH FUND.

The International Growth Fund may not:

(1)  Borrow money except as a temporary measure for extraordinary or emergency
     purposes and then only in an amount up to 10% of the value of its total
     assets (any such borrowing under this section will not be collateralized).
     The portfolio will not borrow for leverage purposes.

(2)  Pledge, mortgage or create a lien on its assets.

(3)  Make loans of money or portfolio securities, except through the purchase of
     debt obligations and repurchase agreements.

(4)  Purchase any securities if, immediately after such purchase, more than 25%
     of the value of the portfolio's total assets would be invested in the
     securities of issuers in the same industry. There is no limitation as to
     the portfolio's investments in obligations issued or guaranteed by the U.S.
     government, its agencies or instrumentalities. For purposes of this
     restriction, the obligations of each foreign government are deemed to
     constitute an industry.

(5)  Invest more than 5% of the value of its total assets in the securities of
     any one issuer or purchase more than 10% of the outstanding voting
     securities, or any class of securities, of any one issuer. For purposes of
     this restriction, all outstanding debt securities of an issuer are
     considered as one class and all preferred stock of an issuer is considered
     as one class. (This restriction does not apply to obligations issued or
     guaranteed by the U.S. government, or its agencies or instrumentalities.)

                                      B-12

<PAGE>   123


(6)  Underwrite securities by others, except to the extent the portfolio may be
     deemed to be an underwriter, under the Federal securities laws, in
     connection with the disposition of portfolio securities.

(7)  Purchase securities of other U.S. or foreign investment companies, except
     that the portfolio may make such a purchase (a) in the open market provided
     that immediately thereafter (i) not more than 10% of the portfolio's total
     assets would be invested in such securities; (ii) not more than 5% of the
     portfolio's total assets would be invested in securities of any one
     investment company; and (iii) not more than 3% of the total outstanding
     voting stock of any one investment company would be owned by the portfolio,
     or (b) as part of an offer of exchange, reorganization or as a dividend.

(8)  Make short sales of securities, or purchase any securities on margin, or
     maintain a short position or participate on a joint or a joint and several
     basis in any trading account in securities, except that the portfolio may
     (i) obtain such short-term credits as may be necessary for the clearance of
     purchases and sales of securities; (ii) purchase or sell futures contracts;
     and (iii) deposit or pay initial or variation margin in connection with
     financial futures contracts or related options transactions.

(9)  Purchase or sell put options, call options, or combinations thereof, except
     that the portfolio may engage in financial futures contracts and related
     options transactions to seek to hedge against either a decline in the value
     of securities included in the portfolio or an increase in the price of
     securities which the portfolio plans to purchase in the future.

(10) Purchase or sell commodities or commodity contracts, except that the
     portfolio may enter into financial futures contracts, options on futures
     contracts and forward foreign currency exchange contracts.

(11) Purchase or sell real estate (although it may purchase securities of
     issuers that engage in real estate operations, securities that are secured
     by interests in real estate or securities that represent interests in real
     estate, including real estate investment trusts).

(12) Invest in interests in oil, gas or other mineral leases, rights or royalty
     contracts or exploration or development programs, although it may invest in
     the securities of issuers which invest in or sponsor such programs.

(13) Invest for the purposes of exercising control or management of another
     issuer.

(14) Issue any "senior securities" as defined in the 1940 Act (except for
     engaging in futures and options transactions and except for borrowing
     subject to the restrictions set forth above).

(15) Invest more than 5% of its total assets in securities of issuers which with
     their predecessors have a record of less than three years' continuous
     operation.

EMERGING MARKETS GROWTH FUND.

The Emerging Markets Growth Fund:

(1)  May not with respect to 75% of its total assets, purchase the securities of
     any issuer (except securities issued or guaranteed by the U.S. government
     or its agencies or instrumentalities) if, as a result, (i) more than 5% of
     the portfolio's total assets would be invested in the securities of that
     issuer or (ii) the portfolio would hold more than 10% of the outstanding
     voting securities of that issuer.

(2)  May (i) borrow money from banks and (ii) make other investments or engage
     in other transactions permissible under the 1940 Act which may involve a
     borrowing, provided that the combination of (i) and (ii) shall not exceed
     331/3% of the value of the portfolio's total assets (including the amount
     borrowed), less the portfolio's liabilities (other than borrowings), or
     such other percentage permitted by law, except that the portfolio may
     borrow up to an additional 5% of its total assets (not including the amount
     borrowed) from a bank for temporary or emergency purposes (but not for
     leverage or the purchase of investments).

                                      B-13

<PAGE>   124





Note: Presently, the Emerging Markets Growth Fund only intends to borrow from
banks for temporary or emergency purposes. However, the portfolio may borrow
money from banks and make other investments or engage in other transactions
permissible under the 1940 Act which may be considered a borrowing (such as
mortgage dollar rolls and reverse repurchase agreements).

(3)  May not issue senior securities, except as permitted under the 1940 Act.

(4)  May not act as an underwriter of another issuer's securities, except to the
     extent that the portfolio may be deemed to be an underwriter within the
     meaning of the Securities Act of 1933 in connection with the purchase and
     sale of portfolio securities.

(5)  May not purchase or sell physical commodities unless acquired as a result
     of ownership of securities or other instruments (but this shall not prevent
     the portfolio from purchasing or selling options, futures contracts, or
     other derivative instruments or from investing in securities or other
     instruments backed by physical commodities).


(6)  May not make loans if, as a result, more than 33 1/3% of the portfolio's
     total assets would be lent to other persons, except through (i) purchases
     of debt securities or other debt instruments or (ii) engaging in repurchase
     agreements.


(7)  May not purchase the securities of any issuer if, as a result, 25% or more
     of the portfolio's total assets would be invested in the securities of
     issuers, the principal business activities of which are in the same
     industry.

(8)  May not purchase or sell real estate unless acquired as a result of
     ownership of securities or other instruments (but this shall not prohibit
     the portfolio from purchasing or selling securities or other instruments
     backed by real estate or of issuers engaged in real estate activities).

The following are the portfolio's non-fundamental operating policies, which may
be changed by the Fund's Board of Directors without shareholder approval.

The Emerging Markets Growth Fund may not:

(9)  Sell securities short, unless the portfolio owns or has the right to obtain
     securities equivalent in kind and amount to the securities sold short, or
     unless it covers such short sale as required by the current rules and
     positions of the Securities and Exchange Commission or its staff and
     provided that transactions in futures contracts or other derivative
     instruments are not deemed to constitute selling securities short.

(10) Purchase securities on margin, except that the Fund may obtain such
     short-term credits as are necessary for the clearance of transactions; and
     provided that margin deposits in connection with futures contracts or other
     derivative instruments shall not constitute purchasing securities on
     margin.

(11) Invest in illiquid securities if, as a result of such investment, more than
     15% of its net assets would be invested in illiquid securities.

(12) Purchase, except for securities acquired as part of a merger, consolidation
     or acquisition of assets, more than 3% of the stock of another investment
     company, except as otherwise permitted by statute, rule, exemptive order,
     SEC no-action letter or investment restriction.

(13) Engage in futures transactions which are impermissible pursuant to Rule 4.5
     under the Commodity Exchange Act and, in accordance with Rule 4.5, will use
     futures transactions solely for bona fide hedging transactions (within the
     meaning of the Commodity Exchange Act); provided, however, that the
     portfolio may, in addition to bona fide hedging transactions, use futures
     transactions if the aggregate initial margin and premiums required to
     establish such positions do not exceed 5% of the portfolio's net assets. In
     addition, the aggregate margin deposits required on all futures
     transactions being held will not exceed 5% of the portfolio's total assets.

                                      B-14

<PAGE>   125

(14) Pledge, mortgage or hypothecate any assets owned by the portfolio except as
     may be necessary in connection with permissible borrowings or investments
     and then such pledging, mortgaging or hypothecating may not exceed 331/3%
     of the portfolio's total assets at the time of the borrowing or investment.

INCOME FUND.

The Income Fund may not:

(1)  Purchase securities of any issuer (other than obligations of, or guaranteed
     by, the United States Government, its agencies or instrumentalities) if, as
     a result, more than 5% of the value of its total assets would be invested
     in securities of that issuer.

(2)  Purchase more than 10% of any class of securities of any issuer, except
     that such restriction shall not apply to securities issued or guaranteed by
     the United States Government, its agencies or instrumentalities. All debt
     securities and all preferred stocks are each considered as one class.

(3)  Invest more than 5% of its total assets in securities of issuers which with
     their predecessors have a record of less than three years' continuous
     operation.

(4)  Make short sales of securities or purchase any securities on margin except
     to obtain such short-term credits as may be necessary for the clearance of
     transactions.

(5)  Write, purchase or sell puts, calls or combinations thereof.

(6)  Invest for the purpose of exercising control or management of another
     issuer.

(7)  Invest in commodities or commodity futures contracts or in real estate,
     although it may invest in securities which are secured by real estate and
     securities of issuers which invest or deal in real estate.

(8)  Invest in interests in oil, gas or other mineral exploration or development
     programs, although it may invest in the securities of issuers which invest
     in or sponsor such programs.

(9)  Underwrite securities issued by others except to the extent the portfolio
     may be deemed to be an underwriter, under the Federal securities laws, in
     connection with the disposition of portfolio securities.

(10) Issue senior securities as defined in the 1940 Act.

(11) Purchase common stocks, preferred stocks, warrants or other equity
     securities.

(12) Make loans to others, except through the purchase of debt obligations or
     repurchase agreements or the loaning of portfolio securities not exceeding
     75% of the value of its total assets.

(13) Borrow money, except as a temporary measure and then only in an amount up
     to 5% of the value of its total assets (any such borrowing under this
     section will not be collateralized). The portfolio will not borrow for
     leverage purposes.

(14) Concentrate more than 25% of the value of its total assets in any one
     industry. This restriction does not apply to U.S. Government securities or
     government agency securities, or to instruments, such as repurchase
     agreements, secured by these instruments.

The following is the portfolio's non-fundamental operating policy, which may be
changed by the Fund's Board of Directors without shareholder approval.

                                      B-15

<PAGE>   126

The Income Fund may not:

(15) Invest in illiquid securities if, as a result of such investment, more than
     15% of its net assets would be invested in illiquid securities.

READY RESERVES FUND.

The Ready Reserves Fund may not:

(1)  Purchase securities of any issuer (other than obligations of, or guaranteed
     by, the United States Government, its agencies or instrumentalities) if, as
     a result, more than 5% of the value of its total assets would be invested
     in securities of that issuer.

(2)  Purchase more than 10% of any class of securities of any issuer, except
     that such restriction shall not apply to securities issued or guaranteed by
     the United States Government, its agencies or instrumentalities. All debt
     securities and all preferred stocks are each considered as one class.

(3)  Invest more than 5% of its total assets in securities of issuers which with
     their predecessors have a record of less than three years' continuous
     operation.

(4)  Make short sales of securities, or purchase any securities on margin except
     to obtain such short-term credits as may be necessary for the clearance of
     transactions.

(5)  Write, purchase or sell puts, calls or combinations thereof.

(6)  Invest for the purpose of exercising control or management of another
     issuer.

(7)  Invest in commodities or commodity futures contracts or in real estate,
     although it may invest in securities which are secured by real estate and
     securities of issuers which invest or deal in real estate.

(8)  Invest in interests in oil, gas or other mineral exploration or development
     programs, although it may invest in the securities of issuers which invest
     in or sponsor such programs.

(9)  Underwrite securities issued by others except to the extent the portfolio
     may be deemed to be an underwriter, under the Federal securities laws, in
     connection with the disposition of portfolio securities.

(10) Issue senior securities as defined in the 1940 Act.

(11) Make loans to others (except through the purchase of debt obligations or
     repurchase agreements in accordance with its investment objective and
     policies).

(12) Borrow money except as a temporary measure for extraordinary or emergency
     purposes and then only in an amount up to 5% of the value of its total
     assets (any such borrowing under this section will not be collateralized).
     The portfolio will not borrow for leverage purposes.

(13) Concentrate more than 25% of the value of its total assets in any one
     industry; provided, however, that the portfolio reserves freedom of action
     to invest up to 100% of its total assets in certificates of deposit, time
     deposits or bankers' acceptances or repurchase agreements with domestic
     branches of domestic banks when management considers it to be in the
     interests of the portfolio in attaining its investment objective.

(14) Invest in securities restricted as to disposition under the Federal
     securities laws (except commercial paper issued under Section 4(2) of the
     Securities Act of 1933).

(15) Purchase securities of other investment companies, except in connection
     with a merger, consolidation, reorganization or acquisition of assets.

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                              INVESTMENT PRACTICES

The Prospectus describes each portfolio's investment objective as well as
certain investment policies and investment techniques that the portfolio may
employ in pursuing its investment objective. The following discussion
supplements the discussion contained in the Prospectus, including the Investment
Glossary at the end of the Prospectus. Not all of the portfolios may invest in
all of the types of investments listed below.

COLLATERALIZED OBLIGATIONS. Mortgage-Backed Securities. Collateralized
obligations include mortgage-backed collateralized obligations ("mortgage-backed
securities"). Mortgage-backed securities are securities that directly or
indirectly represent a participation in, or are secured by and payable from,
mortgage loans secured by real property. There currently are three basic types
of mortgage-backed securities: (1) those issued or guaranteed by the U.S.
Government or one of its agencies or instrumentalities, such as GNMA (Government
National Mortgage Association), FNMA (Federal National Mortgage Association) and
FHLMC (Federal Home Loan Mortgage Corporation); (2) those issued by private
issuers that represent an interest in or are collateralized by mortgage-backed
securities issued or guaranteed by the U.S. Government or one of its agencies or
instrumentalities; and (3) those issued by private issuers that represent an
interest in or are collateralized by whole mortgage loans or mortgage-backed
securities without a government guarantee but that usually have some form of
private credit enhancement.

The yield characteristics of mortgage-backed securities differ from traditional
debt securities. Among the major differences are that interest and principal
payments are made more frequently, usually monthly, and that principal may be
prepaid at any time because the underlying mortgage loans generally may be
prepaid at any time. As a result, if a portfolio purchases such a security at a
premium, a prepayment rate that is faster than expected will reduce yield to
maturity, while a prepayment rate that is slower than expected will increase
yield to maturity. Conversely, if a portfolio purchases these securities at a
discount, faster than expected prepayments will increase yield to maturity,
while slower than expected prepayments will reduce it.

Prepayments on a pool of mortgage loans are influenced by a variety of economic,
geographic, social and other factors, including changes in mortgagors' housing
needs, job transfers, unemployment, mortgagors' net equity in the mortgaged
properties and servicing decisions. Generally, however, prepayments on
fixed-rate mortgage loans will increase during a period of falling interest
rates and decrease during a period of rising interest rates. Accordingly,
amounts available for reinvestment by the portfolio are likely to be greater
during a period of declining interest rates and, as a result, are likely to be
reinvested at lower interest rates than during a period of rising interest
rates. Mortgage-backed securities may decrease in value as a result of increases
in interest rates and may benefit less than other fixed income securities from
declining interest rates because of the risk of prepayment.

Guaranteed Mortgage Pass-Through Securities. Mortgage pass-through securities
represent participation interests in pools of residential mortgage loans
originated by United States Governmental or private lenders and guaranteed, to
the extent provided in such securities, by the United States Government or one
of its agencies or instrumentalities. Such securities, which are ownership
interests in the underlying mortgage loans, differ from conventional debt
securities, which provide for periodic payment of interest in fixed amounts
(usually semi-annually) and principal payments at maturity or on specified call
dates. Mortgage pass-through securities provide for monthly payments that are a
"pass-through" of the monthly interest and principal payments (including any
prepayments) made by the individual borrowers on the pooled mortgage loans, net
of any fees paid to the guarantor of such securities and the services of the
underlying mortgage loans. The guaranteed mortgage pass-through securities in
which the portfolio will invest will include those issued or guaranteed by GNMA,
FNMA and FHLMC.

GNMA is a wholly owned corporate instrumentality of the United States within the
Department of Housing and Urban Development. The National Housing Act of 1934,
as amended (the "Housing Act"), authorizes GNMA to guarantee the timely payment
of the principal of and interest on certificates ("Ginnie Mae Certificates")
that are based upon and backed by a pool of mortgage loans insured by the
Federal Housing Administration under the Housing Act or Title V of the Housing
Act of 1949 (FHA Loans), or guaranteed by the Veterans' Administration under the
Servicemen's Readjustment Act of 1944, as amended (VA Loans), or by pools of
other eligible mortgage loans. Ginnie Mae Certificates represent a pro rata
interest in one or more pools of eligible mortgage loans. The Housing Act
provides that the full faith and credit of the United States Government is
pledged to the payment of all
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amounts that may be required to be paid under any guarantee. In order to meet
its obligations under such guarantee, GNMA is authorized to borrow from the
United States Treasury with no limitations as to amount.

FNMA is a federally chartered and privately owned corporation organized and
existing under the Federal National Mortgage Association Charter Act. FNMA was
originally established in 1938 as a United States Government agency to provide
supplemental liquidity to the mortgage market and was transformed into a
stockholder owned and privately managed corporation by legislation enacted in
1968. FNMA provides funds to the mortgage market primarily by purchasing home
mortgage loans from local lenders, thereby replenishing their funds for
additional lending. FNMA acquires funds to purchase home mortgage loans from
many capital market investors that may not ordinarily invest in mortgage loans
directly, thereby expanding the total amount of funds available for housing.

Each Fannie Mae Certificate will entitle the registered holder thereof to
receive amounts representing the holder's pro rata interest in scheduled
principal payments and interest payments (at such Fannie Mae Certificate's
pass-through rate, which is net of any servicing and guarantee fees on the
underlying mortgage loans) and any principal prepayments, on the mortgage loans
in the pool represented by such Fannie Mae Certificate and such holder's
proportionate interest in the full principal amount of any foreclosed or
otherwise finally liquidated mortgage loan. The full and timely payment of
principal of and interest on each Fannie Mae Certificate will be guaranteed by
FNMA, which guarantee is not backed by the full faith and credit of the United
States Government. FNMA has limited rights to borrow from the United States
Treasury.

FHLMC is a corporate instrumentality of the United States created pursuant to
the Emergency Home Finance Act of 1970, as amended. FHLMC was established
primarily for the purpose of increasing the availability of mortgage credit for
the financing of needed housing. The principal activity of FHLMC currently
consists of the purchase of first lien, conventional, residential mortgage loans
and participation interests in such mortgage loans and the resale of the
mortgage loans so purchased in the form of mortgage securities, primarily
Freddie Mac Certificates.

FHLMC guarantees to each registered holder of a Freddie Mac Certificate the
timely payment of interest at the rate provided for by such Freddie Mac
Certificate, whether or not received. FHLMC also guarantees to each holder of a
Freddie Mac Certificate ultimate collection of all principal of the related
mortgage loans, without any offset or deduction, but does not always guarantee
the timely payment of scheduled principal. FHLMC may remit the amount due on
account of its guarantee of collection of principal at any time after default on
an underlying mortgage loan, but not later than 30 days following (i)
foreclosure sale, (ii) payment of a claim by any mortgage insurer or (iii) the
expiration of any right of redemption, whichever occurs last, but in any event
no later than one year after demand has been made upon the mortgagor for
accelerated payment of principal. The obligations of FHLMC under its guarantee
are obligations solely of FHLMC and are not backed by the full faith and credit
of the United States Government. FHLMC has limited rights to borrow from the
United States Treasury.

Private Mortgage Pass-Through Securities. Private mortgage pass-through
securities ("private pass-throughs") are structured similarly to the Ginnie Mae,
Fannie Mae and Freddie Mac mortgage pass-through securities described above and
are issued by originators of and investors in mortgage loans, including savings
and loan associations, mortgage banks, commercial banks, investment banks and
special purpose subsidiaries of the foregoing. Private pass-throughs are usually
backed by a pool of conventional fixed rate or adjustable rate mortgage loans.
Since private pass-throughs typically are not guaranteed by an entity having the
credit status of GNMA, FNMA or FHLMC, such securities generally are structured
with one or more types of credit enhancement. See "Types of Credit Support,"
below.

Collateralized Mortgage Obligations and Multiclass Pass-Through Securities.
Collateralized mortgage obligations, or "CMOs," are debt obligations
collateralized by mortgage loans or mortgage pass-through securities. Typically,
CMOs are collateralized by Ginnie Mae, Fannie Mae or Freddie Mac Certificates,
but also may be collateralized by whole loans or private pass-throughs (such
collateral collectively hereinafter referred to as "Mortgage Assets").
Multiclass pass-through securities are equity interests in a trust composed of
Mortgage Assets. Payments of principal of and interest on the Mortgage Assets
and any reinvestment income thereon provide the funds to pay debt service on the
CMOs or make scheduled distributions on the multiclass pass-through securities.
CMOs may be issued by agencies or instrumentalities of the United States
Government, or by private originators of, or investors in, mortgage loans,
including savings and loan associations, mortgage banks, commercial banks,
investment banks and special purpose subsidiaries of the foregoing.

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In a CMO, a series of bonds or certificates is issued in multiple classes. Each
class of CMOs, often referred to as a "tranche," is issued at a specific fixed
or floating coupon rate and has a stated maturity or final distribution date.
Principal prepayments on the Mortgage Assets may cause the CMOs to be retired
substantially earlier than their stated maturities or final distribution dates.
Interest is paid or accrues on all classes of the CMOs on a monthly, quarterly
or semi-annual basis. The principal of and interest on the Mortgage Assets may
be allocated among the several classes of a series of a CMO in innumerable ways.
In a common structure, payments of principal, including any principal
prepayments, on the Mortgage Assets are applied to the classes of the series of
a CMO in the order of their respective stated maturities or final distribution
dates, so that no payment of principal will be made on any class of CMOs until
all other classes having an earlier stated maturity or final distribution date
have been paid in full.

Stripped Mortgage-Backed Securities. Stripped mortgage-backed securities
("SMBS") are derivative multiclass mortgage securities. SMBS may be issued by
agencies or instrumentalities of the United States Government, or by private
originators of, or investors in, mortgage loans, including savings and loan
associations, mortgage banks, commercial banks, investment banks and special
purpose subsidiaries of the foregoing.

SMBS are usually structured with two classes that receive different proportions
of the interest and principal distributions on a pool of Mortgage Assets. A
common type of SMBS will have one class receiving some of the interest and most
of the principal from the Mortgage Assets, while the other class will receive
most of the interest and the remainder of the principal. In the most extreme
case, one class will receive all the interest (the interest-only or "IO" class),
while the other class will receive all the principal (the principal-only or "PO"
class). The yield to maturity on an IO class is extremely sensitive to the rate
of principal payments (including prepayments) on the related underlying Mortgage
Assets and a rapid rate of principal payments may have a material adverse effect
on the portfolio's yield to maturity. If the underlying Mortgage Assets
experience greater than anticipated prepayments of principal, the portfolio may
fail to fully recoup its initial investment in these securities.

Although SMBS are purchased and sold by institutional investors through several
investment banking firms acting as brokers or dealers, these securities were
only recently developed and, accordingly, may have less liquidity than other
securities. The portfolio will invest only in IO and PO class mortgage
obligations collateralized by securities guaranteed by the United States
Government.

Types of Credit Support. Mortgage-backed and asset-backed securities are often
backed by a pool of assets representing the obligations of a number of different
parties. To lessen the effect of failures by obligors on underlying assets to
make payments, such securities may contain elements of credit support. Such
credit support falls into two categories: (i) liquidity protection and (ii)
protection against losses resulting from ultimate default by an obligor on the
underlying assets. Liquidity protection refers to the provision of advances,
generally by the entity administering the pool of assets, to ensure that the
receipt of payments on the underlying pool occurs in a timely fashion.
Protection against losses resulting from ultimate default ensures ultimate
payment of the obligations on at least a portion of the assets in the pool. Such
protection may be provided through guarantees, insurance policies or letters of
credit obtained by the issuer or sponsor from third parties, through various
means of structuring the transaction or through a combination of such
approaches.

Examples of credit support arising out of the structure of the transaction
include "senior-subordinated securities" (multiple class securities with one or
more classes subordinate to other classes as to the payment of principal thereof
and interest thereon, with the result that defaults on the underlying assets are
borne first by the holders of the subordinated class), creation of "reserve
funds" (where cash or investments, sometimes funded from a portion of the
payments on the underlying assets, are held in reserve against future losses)
and "overcollateralization" (where the scheduled payments on, or the principal
amount of, the underlying assets exceeds that required to make payment of the
securities and pay any servicing or other fees). The degree of credit support
provided for each issue is generally based upon historical information
respecting the level of credit risk associated with the underlying assets.
Delinquency or loss in excess of that anticipated could adversely affect the
return on an investment in such a security.

Asset-Backed Securities. The securitization techniques used to develop
mortgage-backed securities are now being applied to a broad range of assets.
Through the use of trusts and special purpose corporations, various types of
assets, primarily automobile and credit card receivables, are being scrutinized
in pass-through structures similar to

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the mortgage pass-through structures described above or in a pay-through
structure similar to the CMO structure. The Income Fund may invest in these and
other types of asset-backed securities that may be developed in the future.

As with mortgage-backed securities, the yield characteristics of asset-backed
securities differ from traditional debt securities. As with mortgage-backed
securities, asset-backed securities are often backed by a pool of assets
representing the obligations of a number of different parties and use similar
credit enhancement techniques. See "Mortgage-Backed Securities," above. In
general, however, the collateral supporting asset-backed securities is of
shorter maturity than mortgage loans and is less likely to experience
substantial prepayments. Although certain of the factors that affect the rate of
prepayments on mortgage-backed securities also affect the rate of prepayments on
asset-backed securities, during any particular period, the predominant factors
affecting prepayment rates on mortgage-backed securities and asset-backed
securities may be different.

Asset-backed securities present certain risks that are not presented by
mortgage-backed securities. Primarily, these securities do not have the benefit
of the same security interest in the related collateral. Credit card receivables
are generally unsecured and the debtors are entitled to the protection of a
number of state and federal consumer credit laws, many of which give such
debtors the right to set off certain amounts owed on the credit cards, thereby
reducing the balance due. Most issuers of automobile receivables permit the
services to retain possession of the underlying obligations. If the servicers
were to sell these obligations to another party, there is a risk that the
purchaser would acquire an interest superior to that of the holders of the
related automobile receivables. In addition, because of the large number of
vehicles involved in a typical issuance and technical requirements under state
laws, the trustee for the holders of the automobile receivables may not have a
proper security interest in all the obligations backing such receivables.
Therefore, there is the possibility that recoveries on repossessed collateral
may not, in some cases, be available to support payments on these securities.

Inverse Floaters. The Income Fund may invest in mortgage derivative products
like inverse floating rate debt instruments ("inverse floaters"). The interest
rate on an inverse floater resets in the opposite direction from the market rate
of interest to which the inverse floater is indexed. The income from an inverse
floater may be magnified to the extent that its rate varies by a magnitude that
exceeds the magnitude of the change in the index rate of interest. The higher
the degree of magnification in an inverse floater, the greater the volatility in
its market value. Accordingly, the duration of an inverse floater may exceed its
stated final maturity. The coupon of an inverse floating rate note moves
inversely to the movement of interest rates. In addition, mortgage-backed
inverse floaters will experience approximately the same changes in average lives
and durations that other comparable fixed-rate mortgage-backed bonds do when
prepayments rise and fall with declines and increases in interest rates. In a
rising interest rate environment, the declining coupon coupled with the increase
in the average life can magnify the price decline relative to a fixed-rate
obligation. Conversely, rate declines increase coupon income and gradually
shorten the average life, which tends to amplify the price increase. Inverse
floaters are typically priced based on a matrix.

FOREIGN SECURITIES. Investing in foreign securities involves a series of risks
not present in investing in U.S. securities. Most of the foreign securities
held by the portfolios will not be registered with the Securities and Exchange
Commission (the "SEC"), nor will the foreign issuers be subject to SEC
reporting requirements. Accordingly, there may be less publicly available
information concerning foreign issuers of securities held by the portfolio than
is available concerning U.S. companies. Disclosure and regulatory standards in
many respects are less stringent in emerging market countries than in the U.S.
and other major markets. There also may be a lower level of monitoring and
regulation of emerging markets and the activities of investors in such markets
and enforcement of existing regulations may be extremely limited. Foreign
companies and, in particular, companies in smaller and emerging capital markets
are not generally subject to uniform accounting, auditing and financial
reporting standards, or to other regulatory requirements comparable to those
applicable to U.S. companies. The portfolio's net investment income and capital
gains from its foreign investment activities may be subject to non-U.S.
withholding taxes.

The costs attributable to foreign investing that the portfolio must bear
frequently are higher than those attributable to domestic investing; this is
particularly true with respect to emerging capital markets. For example, the
costs of maintaining custody of foreign securities exceeds custodian costs for
domestic securities and transaction and settlement costs of foreign investing
also frequently are higher than those attributable to domestic investing. Costs
associated with the exchange of currencies also make foreign investing more
expensive than domestic investing. Investment income on certain foreign
securities in which the portfolio may invest may be subject to foreign

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withholding or other government taxes that could reduce the return of these
securities. Tax treaties between the United States and foreign countries,
however, may reduce or eliminate the amount of foreign tax to which the
portfolio would be subject.

The economies of individual emerging market countries may differ favorably or
unfavorably from the U.S. economy in such respects as growth of gross domestic
product, rate of inflation, currency depreciation, capital reinvestment,
resource self-sufficiency and balance of payments position. Further, the
economies of developing countries generally are heavily dependent upon
international trade and, accordingly, have been and may continue to be adversely
affected by trade barriers, exchange controls, managed adjustments in relative
currency values and other protectionist measures imposed or negotiated by the
countries with which they trade. These economies also have been and may continue
to be adversely affected by economic conditions in the countries with which they
trade.

Investments in companies domiciled in developing countries may be subject to
potentially higher risks than investments in developed countries. These risks
include (i) less social, political and economic stability; (ii) the small
current size of the markets for such securities and the currently low or
nonexistent volume of trading, which result in a lack of liquidity and in
greater price volatility; (iii) certain national policies which may restrict a
portfolio's investment opportunities, including restrictions on investment in
issuers or industries deemed sensitive to national interests; (iv) the absence
of developed legal structures governing private or foreign investment or
allowing for judicial redress for injury to private property; (v) the absence,
until recently in certain Eastern European countries, of a capital market
structure or market-oriented economy; and (vi) the possibility that recent
favorable economic developments in Eastern Europe may be slowed or reversed by
unanticipated political or social events in such countries.

In addition, many countries in which the portfolios may invest have experienced
substantial, and in some periods extremely high, rates of inflation for many
years. Inflation and rapid fluctuations in inflation rates have had and may
continue to have negative effects on the economies and securities markets of
certain countries. Moreover, the economies of some developing countries may
differ favorably or unfavorably from the U.S. economy in such respects as growth
of gross domestic product, rate of inflation, currency depreciation, capital
reinvestment, resources self-sufficiency and balance of payments position.

Investments in Eastern European countries may involve risks of nationalization,
expropriation and confiscatory taxation. The communist governments of a number
of Eastern European countries expropriated large amounts of private property in
the past, in many cases without adequate compensation, and there can be no
assurance that such expropriation will not occur in the future. In the event of
such expropriation, a portfolio could lose a substantial portion of any
investments it has made in the affected countries. Finally, even though certain
Eastern European currencies may be convertible into U.S. dollars, the conversion
rates may be artificial to the actual market values and may be adverse to
portfolio shareholders. Further, no accounting standards exist in Eastern
European countries.

Investing in Russian securities involves a high degree of risk and special
considerations not typically associated with investing in the U.S. securities
markets, and should be considered highly speculative. Such risks include: (1)
delays in settling portfolio transactions and risk of loss arising out of
Russia's system of share registration and custody; (2) the risk that it may be
impossible or more difficult than in other countries to obtain and/or enforce a
judgment; (3) pervasiveness of corruption and crime in the Russian economic
system; (4) currency exchange rate volatility and the lack of available currency
hedging instruments; (5) higher rates of inflation (including the risk of social
unrest associated with periods of hyper-inflation); (6) controls on foreign
investment and local practices disfavoring foreign investors and limitations on
repatriation of invested capital, profits and dividends, and on a portfolio's
ability to exchange local currencies for U.S. dollars; (7) the risk that the
government of Russia or other executive or legislative bodies may decide not to
continue to support the economic reform programs implemented since the
dissolution of the Soviet Union and could follow radically different political
and/or economic policies to the detriment of investors, including
non-market-oriented policies such as the support of certain industries at the
expense of other sectors or investors, or a return to the centrally planned
economy that existed prior to the dissolution of the Soviet Union; (8) the
financial condition of Russian companies, including large amounts of
inter-company debt which may create a payments crisis on a national scale; (9)
dependency on exports and the corresponding importance of international trade;
(10) the risk that the Russian tax system will not be reformed to prevent
inconsistent, retroactive and/or exorbitant taxation; and (11) possible
difficulty in identifying a purchaser of securities held by a portfolio due to
the underdeveloped nature of the securities markets.


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There is little historical data on Russian securities markets because they are
relatively new and a substantial proportion of securities transactions in Russia
are privately negotiated outside of stock exchanges. Because of the recent
formation of the securities markets as well as the underdeveloped state of the
banking and telecommunications systems, settlement, clearing and registration of
securities transactions are subject to significant risks. Ownership of shares
(except where shares are held through depositories that meet the requirements of
the 1940 Act) is defined according to entries in the company's share register
and normally evidenced by extracts from the register or by formal share
certificates. However, there is no central registration system for shareholders
and these services are carried out by the companies themselves or by registrars
located throughout Russia. These registrars are not necessarily subject to
effective state supervision and it is possible for a portfolio to lose its
registration through fraud, negligence or even mere oversight. While each
portfolio will endeavor to ensure that its interest continues to be
appropriately recorded either itself or through a custodian or other agent
inspecting the share register and by obtaining extracts of share registers
through regular confirmations, these extracts have no legal enforceability and
it is possible that subsequent illegal amendment or other fraudulent act may
deprive the portfolio of its ownership rights or improperly dilute its
interests. In addition, while applicable Russian regulations impose liability on
registrars for losses resulting from their errors, it may be difficult for a
portfolio to enforce any rights it may have against the registrar or issuer of
the securities in the event of loss of share registration. Furthermore, although
a Russian public enterprise with more than 1,000 shareholders is required by law
to contract out the maintenance of its shareholder register to an independent
entity that meets certain criteria, in practice this regulation has not always
been strictly enforced. Because of this lack of independence, management of a
company may be able to exert considerable influence over who can purchase and
sell the company's shares by illegally instructing the registrar to refuse to
record transactions in the share register. This practice may prevent a portfolio
from investing in the securities of certain Russian issuers deemed suitable by
its portfolio manager. Further, this also could cause a delay in the sale of
Russian securities by a portfolio if a potential purchaser is deemed unsuitable,
which may expose the portfolio to potential loss on the investment.

Each portfolio endeavors to buy and sell foreign currencies on as favorable a
basis as practicable. Some price spread in currency exchange (to cover service
charges) will be incurred, particularly when a portfolio changes investments
from one country to another or when proceeds of the sale of shares in U.S.
dollars are used for the purchase of securities in foreign countries. Also, some
countries may adopt policies which would prevent a portfolio from transferring
cash out of the country or withhold portions of interest and dividends at the
source. There is the possibility of cessation of trading on national exchanges,
expropriation, nationalization or confiscatory taxation, withholding and other
foreign taxes on income or other amounts, foreign exchange controls (which may
include suspension of the ability to transfer currency from a given country),
default in foreign government securities, political or social instability, or
diplomatic developments which could affect investments in securities of issuers
in foreign nations.

Foreign markets also have different clearance and settlement procedures and in
certain markets there have been times when settlements have failed to keep pace
with the volume of securities transactions, making it difficult to conduct such
transactions. Delays in settlement could result in temporary periods when assets
of the portfolio are uninvested and no return is earned thereon. The inability
of the portfolio to make intended security purchases due to settlement problems
could cause the portfolio to miss investment opportunities. Inability to dispose
of a portfolio security due to settlement problems either could result in losses
to the portfolio due to subsequent declines in the value of such portfolio
security or, if the portfolio has entered into a contract to sell the security,
could result in possible liability to the purchaser.

Foreign securities may be purchased through depository receipts, including
American Depository Receipts ("ADRs"), European Depository Receipts ("EDRs")
Global Depository Receivables ("GDRs"), or other securities convertible into
securities of foreign issuers. These securities may not necessarily be
denominated in the same currency as the securities into which they may be
converted. Generally, ADRs, in registered form, are denominated in U.S. dollars
and are designed for use in the U.S. securities markets, while EDRs and GDRs may
be denominated in other currencies and are designed for use in the European
securities markets. ADRs are receipts typically issued by a U.S. bank or trust
company evidencing ownership of the underlying securities. EDRs and GDRs are
European receipts evidencing a similar arrangement. For purposes of the
portfolio's investment policies, ADRs, EDRs and GDRs are deemed to have the same
classification as the underlying securities they represent, except that ADRs,
EDRs and GDRs shall be treated as indirect foreign investments. Thus, an ADR,
EDR or GDR representing

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ownership of common stock will be treated as common stock. ADR, EDR and GDR
depository receipts do not eliminate all of the risks associated with directly
investing in the securities of foreign issuers.

ADR facilities may be established as either "unsponsored" or "sponsored." While
ADRs issued under these two types of facilities are in some respects similar,
there are distinctions between them relating to the rights and obligations of
ADR holders and the practices of market participants.

A depository may establish an unsponsored facility without participation by (or
even necessarily the acquiescence of) the issuer of the deposited securities,
although typically the depository requests a letter of non-objection from such
issuer prior to the establishment of the facility. Holders of unsponsored ADRs
generally bear all the costs of such facilities. The depository usually charges
fees upon the deposit and withdrawal of the deposited securities, the conversion
of dividends into U.S. dollars, the disposition of non-cash distributions and
the performance of other services. The depository of an unsponsored facility
frequently is under no obligation to pass through voting rights to ADR holders
with respect to the deposited securities. In addition, an unsponsored facility
is generally not obligated to distribute communications received from the issuer
of the deposited securities or to disclose material information about such
issuer in the U.S. and thus there may not be a correlation between such
information and the market value of the depository receipts.

Sponsored ADR facilities are created in generally the same manner as unsponsored
facilities, except that the issuer of the deposited securities enters into a
deposit agreement with the depository. The deposit agreement sets out the rights
and responsibilities of the issuer, the depository and the ADR holders. With
sponsored facilities, the issuer of the deposited securities generally will bear
some of the costs relating to the facility (such as dividend payment fees of the
depository), although ADR holders continue to bear certain other costs (such as
deposit and withdrawal fees). Under the terms of most sponsored arrangements,
depositories agree to distribute notices of shareholder meetings and voting
instructions and to provide shareholder communications and other information to
the ADR holders at the request of the issuer of the deposited securities.

FORWARD FOREIGN CURRENCY TRANSACTIONS. The foreign securities held by the
International Growth Fund and the Emerging Markets Growth Fund will usually be
denominated in foreign currencies and the portfolio may temporarily hold foreign
currency in connection with such investments. As a result, the value of the
assets held by the portfolio may be affected favorably or unfavorably by changes
in foreign currency exchange rates, by exchange control regulations and by
indigenous economic and political developments. Some countries in which the
portfolios may invest may also have fixed or managed currencies that are not
free-floating against the U.S. dollar. Further, certain currencies may not be
internationally traded. Certain of these currencies have experienced a steady
devaluation relative to the U.S. dollar. Any devaluations in the currencies in
which a portfolio's securities are denominated may have a detrimental impact on
that portfolio.

The portfolio may enter into forward foreign currency contracts ("forward
currency contracts") in an effort to control some of the uncertainties of
foreign currency rate fluctuations. A forward currency contract is an agreement
to purchase or sell a specific currency at a specified future date and price
agreed to by the parties at the time of entering into the contract. The
portfolio will not engage in foreign currency contracts in which the specified
future date is more than one year from the time of entering into the contract.
In addition, the portfolio will not engage in forward currency contracts for
speculation, but only as an attempt to hedge against changes in foreign currency
exchange rates affecting the values of securities which the portfolio holds or
intends to purchase. Thus, the portfolio will not enter into a forward currency
contract if such contract would obligate the portfolio to deliver an amount of
foreign currency in excess of the value of the portfolio securities or other
assets denominated in that currency.

The International Growth Fund and the Emerging Markets Growth Fund may use
forward currency contracts to fix the value of certain securities it has agreed
to buy or sell. For example, when the portfolio enters into a contract to
purchase or sell securities denominated in a particular foreign currency, the
portfolio could effectively fix the maximum cost of those securities by
purchasing or selling a foreign currency contract, for a fixed value of another
currency, in the amount of foreign currency involved in the underlying
transaction. In this way, the portfolio can protect the value of securities in
the underlying transaction from an adverse change in the exchange rate between
the currency of the underlying securities in the transaction and the currency
denominated in the foreign currency

                                      B-23

<PAGE>   134

contract, during the period between the date the security is purchased or sold
and the date on which payment is made or received.

The International Growth Fund and the Emerging Markets Growth Fund may also use
forward currency contracts to hedge the value, in U.S. dollars, of securities it
currently owns. For example, if the portfolio held securities denominated in a
foreign currency and anticipated a substantial decline (or increase) in the
value of that currency against the U.S. dollar, the portfolio may enter into a
foreign currency contract to sell (or purchase), for a fixed amount of U.S.
dollars, the amount of foreign currency approximating the value of all or a
portion of the securities held which are denominated in such foreign currency.

Upon the maturity of a forward currency transaction, the portfolio may either
accept or make delivery of the currency specified in the contract or, at any
time prior to maturity, enter into a closing transaction which involves the
purchase or sale of an offsetting contract. An offsetting contract terminates
the portfolio's contractual obligation to deliver the foreign currency pursuant
to the terms of the forward currency contract by obligating the portfolio to
purchase the same amount of the foreign currency, on the same maturity date and
with the same currency trader, as specified in the forward currency contract.
The portfolio realizes a gain or loss as a result of entering into such an
offsetting contract to the extent the exchange rate between the currencies
involved moved between the time of the execution of the original forward
currency contract and the offsetting contract.

The use of forward currency contracts to protect the value of securities against
the decline in the value of a currency does not eliminate fluctuations in the
underlying prices of the securities the portfolio owns or intends to acquire,
but it does fix a future rate of exchange. Although such contracts minimize the
risk of loss resulting from a decline in the value of the hedged currency, they
also limit the potential for gain resulting from an increase in the value of the
hedged currency. The benefits of forward currency contracts to the portfolio
will depend on the ability of the portfolio's investment manager to accurately
predict future currency exchange rates.

FOREIGN CURRENCY FUTURES. Generally, foreign futures contracts will be executed
on a U.S. exchange. To the extent they are not, however, engaging in such
transactions will involve the execution and clearing of trades on or subject to
the rules of a foreign board of trade. Neither the National Futures Association
nor any domestic (U.S.) exchange regulates activities of any foreign boards of
trade, including the execution, delivery and clearing of transactions, or has
the power to compel enforcement of the rules of a foreign board of trade or any
applicable foreign law. This is true even if the exchange is formally linked to
a domestic market so that a position taken on the exchange may be liquidated by
a transaction on the appropriate domestic market. Moreover, applicable laws or
regulations will vary depending on the foreign country in which the foreign
futures transaction occurs. Therefore, entities (such as the portfolio) which
trade foreign futures contracts may not be afforded certain of the protective
measures provided by the Commodity Exchange Act, Commodity Futures Trading
Commission ("CFTC") regulations, the rules of the National Futures Association
or those of a domestic (U.S.) exchange. In particular, monies received from
customers for foreign futures transactions may not be provided the same
protections as monies received in connection with transactions on U.S. futures
exchanges. In addition, the price of any foreign futures and, therefore, the
potential profits and loss thereon, may be affected by any variance in the
foreign exchange rate between the time the order for the futures contract is
placed and the time it is liquidated, offset or exercised.

FUTURES. The Value Discovery Fund may purchase and sell futures contracts on
domestic stock indexes in order to facilitate exposure to the market or in order
to help meet redemption requests. The portfolio may purchase and sell futures
contracts on stock indexes, such as the Russell 2000 Index, as a substitute for
purchasing or selling the underlying securities. The portfolio may not purchase
or sell a futures contract unless, immediately after any such transaction, the
sum of the aggregate amount of initial margin deposits on its existing futures
positions is 5% or less of its total assets (after taking into account certain
technical adjustments).

The Value Discovery Fund may be subject to additional risks associated with
futures contracts, such as the possibility that the Adviser's forecasts of
market values and other factors are not correct, imperfect correlation between
the hedging instrument and the asset or liability being hedged, default by the
other party to the transaction and inability to close out a position because of
the lack of a liquid market. In addition to the possibility that there may be an
imperfect correlation, or no correlation at all, between movements in a futures
contract and the securities being hedged, the price of futures contracts may not
correlate perfectly with movement in the cash market due to

                                      B-24

<PAGE>   135




certain market distortions. As a result of these factors, a correct forecast of
general market trends or interest rate movements by the Adviser may still not
result in a successful hedging transaction over a short time frame.

The transactions described above are frequently referred to as derivative
transactions. In general, derivatives are instruments whose value is based upon,
or derived from, some underlying index, reference rate (e.g., interest rates or
currency exchange rates), security, commodity or other asset.

HIGH-YIELD/HIGH-RISK SECURITIES. High-yield/high-risk securities (or "junk"
bonds) are debt securities rated below investment grade by the primary rating
agencies (such as Standard & Poor's Ratings Services and Moody's Investors
Service, Inc.).

The value of lower quality securities generally is more dependent on the ability
of the issuer to meet interest and principal payments (i.e., credit risk) than
is the case for higher quality securities. Conversely, the value of higher
quality securities may be more sensitive to interest rate movements than lower
quality securities. Issuers of high-yield securities may not be as strong
financially as those issuing bonds with higher credit ratings. Investments in
such companies are considered to be more speculative than higher quality
investments.

Issuers of high-yield securities are more vulnerable to real or perceived
economic changes (for instance, an economic downturn or prolonged period of
rising interest rates), political changes or adverse developments specific to
the issuer. The market for lower quality securities is generally less liquid
than the market for higher quality securities. Adverse publicity and investor
perceptions as well as new or proposed laws may also have a greater negative
impact on the market for lower quality securities.

INVESTMENT COMPANIES. The Fund has applied for certain exemptive relief with the
SEC that, if granted, will allow the portfolios to invest a portion of their
assets into shares of the Ready Reserves Fund based upon the terms and
conditions of such relief.

ILLIQUID SECURITIES. Illiquid securities are securities that are not readily
marketable. The Board of Directors of the Fund, or its delegate, has the
ultimate authority to determine, to the extent permissible under the federal
securities laws, which securities are illiquid for purposes of this limitation.
Certain securities exempt from registration or issued in transactions exempt
from registration under the Securities Act of 1933, as amended (the "Securities
Act"), such as securities that may be resold to institutional investors under
Rule 144A under the Securities Act and Section 4(2) commercial paper may be
considered liquid under guidelines adopted by the Fund's Board of Directors.

The Board of Directors has delegated to the Adviser the day-to-day determination
of the liquidity of a security, although it has retained oversight for such
determinations. The Board of Directors has approved procedures that allow the
Adviser to deem Section 4(2) commercial paper liquid only if the Adviser
determines that there is no significant difference between Section 4(2)
commercial paper and traditional commercial paper based upon an evaluation of
the following characteristics: (i) market characteristic, such as the nature of
the security and the nature of marketplace trades; (ii) trading characteristics,
such as the frequency of trades and quotes for the security, the number of
dealers willing to purchase or sell the security and the number of other
potential purchasers; and (iii) the quality of the issue or issuer. With respect
to a portfolio's foreign holdings, a foreign security may be considered liquid
by the Adviser (despite its restricted nature under the Securities Act) if the
security can be freely traded in a foreign securities market and the facts and
circumstances support a finding of liquidity.

LENDING. The Income Fund may from time to time lend securities (but not in
excess of 75% of its assets) from its portfolio to brokers, dealers and
financial institutions, provided: (1) the loan is secured continuously by
collateral consisting of U.S. Government securities, government agency
securities, U.S. Government instrumentality securities, cash or cash equivalents
adjusted daily to have a market value at least equal to the current market value
of the securities loaned plus accrued interest; (2) the portfolio may at any
time call the loan and regain the securities loaned; and (3) the Adviser (under
the supervision of the Board of Directors) has reviewed the creditworthiness of
the borrower and has found it satisfactory. The portfolio will receive from the
borrower amounts equal to the interest paid on the securities loaned and will
also earn income for having made the loan. Any cash collateral will be invested
in short-term securities, the income from which will increase the return to the
portfolio. The risks

                                      B-25

<PAGE>   136




associated with lending portfolio securities are similar to those of entering
into repurchase agreements. While the Value Discovery Fund has the authority to
lend portfolio securities, it has no current intention to do so.

REPURCHASE AGREEMENTS. In a repurchase agreement, a portfolio buys a security at
one price and at the time of sale, the seller agrees to repurchase the
obligation at a mutually agreed upon time and price (usually within seven days).
The repurchase agreement thereby determines the yield during the purchaser's
holding period, while the seller's obligation to repurchase is secured by the
value of the underlying security. The Adviser will monitor, on an ongoing basis,
the value of the underlying securities to ensure that the value always equals or
exceeds the repurchase price plus accrued interest. Repurchase agreements could
involve certain risks in the event of a default or insolvency of the other party
to the agreement, including possible delays or restrictions upon a portfolio's
ability to dispose of the underlying securities. The risk to a portfolio is
limited to the ability of the seller to pay the agreed upon sum on the delivery
date. In the event of default, a repurchase agreement provides that the
portfolio is entitled to sell the underlying collateral. The loss, if any, to
the portfolio will be the difference between the proceeds from the sale and the
repurchase price. However, if bankruptcy proceedings are commenced with respect
to the seller of the security, disposition of the collateral by the portfolio
may be delayed or limited. Although no definitive creditworthiness criteria are
used, the Adviser reviews the creditworthiness of the banks and non-bank dealers
with which the portfolio enters into repurchase agreements to evaluate those
risks. The Board of Directors will review and monitor the creditworthiness of
broker-dealers and banks with which a portfolio enters into repurchase
agreements. A portfolio may, under certain circumstances, deem repurchase
agreements collateralized by U.S. government securities to be investments in
U.S. government securities.

RESTRICTED SECURITIES. Restricted securities may be sold only in privately
negotiated transactions or in a public offering with respect to which a
registration statement is in effect under the Securities Act. Where registration
is required, a portfolio may be obligated to pay all or part of the registration
expenses and a considerable period may elapse between the time of the decision
to sell and the time the portfolio may be permitted to sell a security under an
effective registration statement. If, during such a period, adverse market
conditions were to develop, the portfolio might obtain a less favorable price
than prevailed when it decided to sell. If through the appreciation of
restricted securities or the depreciation of unrestricted securities, a
portfolio would be in a position where more of its net assets are invested in
illiquid securities, including restricted securities that are not readily
marketable (except for 144A Securities and 4(2) commercial paper deemed to be
liquid by the Adviser), than is permitted by its investment restrictions, the
Fund will take such steps as it deems advisable, if any, to protect liquidity.

SMALL COMPANIES. While smaller companies generally have the potential for rapid
growth, investments in smaller companies often involve greater risks than
investments in larger, more established companies because smaller companies may
lack the management experience, financial resources, product diversification and
competitive strengths of larger companies. In addition, in many instances the
securities of smaller companies are traded only over-the-counter or on a
regional securities exchange and the frequency and volume of their trading is
substantially less than is typical of larger companies. Therefore, the
securities of smaller companies may be subject to greater and more abrupt price
fluctuations. When making large sales, the portfolio may have to sell portfolio
holdings at discounts from quoted prices or may have to make a series of small
sales over an extended period of time due to the trading volume of smaller
company securities. Investors should be aware that, based on the foregoing
factors, an investment in the Value Discovery Fund and the Emerging Markets
Growth Fund, and to a lesser extent, the Growth Fund and the International
Growth Fund, may be subject to greater price fluctuations than an investment in
a fund that invests primarily in larger, more established companies. The
Adviser's research efforts may also play a greater role in selecting securities
for the portfolio than in a fund that invests in larger, more established
companies.

WARRANTS. Warrants are securities giving the holder the right, but not the
obligation, to buy the stock of an issuer at a given price (generally higher
than the value of the stock at the time of issuance) during a specified period
or perpetually. Warrants may be acquired separately or in connection with the
acquisition of securities. Warrants do not carry with them the right to
dividends or voting rights with respect to the securities that they entitle
their holder to purchase and they do not represent any rights in the assets of
the issuer. As a result, warrants may be considered to have more speculative
characteristics than certain other types of investments. In addition, the value
of a warrant does not necessarily change with the value of the underlying
securities and a warrant ceases to have value if it is not exercised prior to
its expiration date.

                                      B-26

<PAGE>   137

WHEN-ISSUED OR DELAYED DELIVERY TRANSACTIONS. Each portfolio may purchase newly
issued securities on a when-issued basis and may purchase or sell portfolio
securities on a delayed delivery basis. When a portfolio purchases securities on
a when-issued or a delayed delivery basis, it becomes obligated to purchase the
securities and it has all the rights and risks attendant to ownership of the
securities, although delivery and payment occur at a later date. A portfolio
will record the transaction and reflect the liability for the purchase and the
value of the security in determining its net asset value. The value of
fixed-income securities to be delivered in the future will fluctuate as interest
rates vary. A portfolio generally has the ability to close out a purchase
obligation on or before the settlement date, rather than take delivery of the
security.

At the time a portfolio makes the commitment to sell a security on a delayed
delivery basis, it will record the transaction and include the proceeds to be
received in determining its net asset value; accordingly, any fluctuations in
the value of the security sold pursuant to a delayed delivery commitment are
ignored in calculating net asset value so long as the commitment remains in
effect. Normally, settlement occurs within one month of the purchase or sale.

To the extent a portfolio engages in when-issued or delayed delivery purchases,
it will do so for the purpose of acquiring securities consistent with the
portfolio's investment objective and policies and not for the purpose of
investment leverage or to speculate on interest rate changes, but each portfolio
reserves the right to sell these securities before the settlement date if deemed
advisable. To the extent required to comply with Securities and Exchange
Commission Release No. IC-10666, when purchasing securities on a when-issued or
delayed delivery basis, each portfolio will maintain in a segregated account
cash or liquid securities equal to the value of such contracts.


                  PURCHASE, REPURCHASE AND REDEMPTION OF SHARES



PURCHASE OF SHARES--ALTERNATIVE PURCHASE ARRANGEMENTS. Class A shares of each
Fund (except Ready Reserves) are sold to investors subject to an initial sales
charge. Class B shares are sold without an initial sales charge but are subject
to higher ongoing expenses than Class A shares and a contingent deferred sales
charge payable upon certain redemptions. Class B shares automatically convert to
Class A shares at the end of the seventh year after issuance. Class C shares are
sold without an initial sales charge but are subject to higher ongoing expenses
than Class A shares, [are subject to a contingent deferred sales charge payable
upon certain redemptions within the first year following purchase,] and do not
convert into another class. Class R and Class I shares are sold to investors
without an initial sales charge or a contingent deferred sales charge, and have
lower ongoing expenses than Class A shares. When placing purchase orders,
investors must specify whether the order is for Class A, Class B, Class C
shares, Class R shares or Class I shares.



The primary distinctions among the classes of each Fund's shares lie in their
initial and contingent deferred sales charge structure and in their ongoing
expenses, including asset-based sales charges in the form of Rule 12b-1
distribution fees and shareholder services fees. These differences are
summarized in the table below. See, also, "Summary of Expenses," Each class has
distinct advantages and disadvantages for different investors, and investors may
choose the class that best suits their circumstances and objectives.



<TABLE>
<CAPTION>

                                                           ANNUAL                 ANNUAL
                                                         12B-1 FEES             SHAREHOLDER
                                                         (AS A % OF            SERVICES FEES
                                                        AVERAGE DAILY       (AS A % OF AVERAGE
                           SALES CHARGE                  NET ASSETS)         DAILY NET ASSETS)    OTHER INFORMATION
                           ------------                  -----------         -----------------    -----------------
<S>            <C>                                      <C>                 <C>                 <C>
Class A         Maximum initial sales charge of             None                   0.25%        Initial sales charge
                5.75% (2.00% for the Income                                                     waived or reduced
                Fund) of the public offering price                                              for certain
                                                                                                purchases
</TABLE>


                                      B-27

<PAGE>   138




<TABLE>
<CAPTION>

                                                           ANNUAL                 ANNUAL
                                                         12B-1 FEES             SHAREHOLDER
                                                         (AS A % OF            SERVICES FEES
                                                        AVERAGE DAILY       (AS A % OF AVERAGE
                           SALES CHARGE                  NET ASSETS)         DAILY NET ASSETS)    OTHER INFORMATION
                           ------------                  -----------         -----------------    -----------------
<S>            <C>                                      <C>                 <C>                 <C>
Class B         Maximum contingent deferred                 0.75%                  0.25%        Shares convert to
                sales charge of 5.00% (2.00% for                                                Class A shares eight
                the Income Fund) of redemption                                                  (three for the
                proceeds; declines to zero after six                                            Income Fund) years
                years (two years for the Income                                                 after issuance
                Fund)

Class C         Contingent deferred sales charge of         0.75%                  0.25%        No conversion
                1% of redemption proceeds for                                                   feature
                redemptions made during first year
                after purchase

Class R         None                                        None                   None

Class I         None                                        None                   None
</TABLE>



ELIGIBILITY

Class I shares are available for purchase exclusively by the following
categories of institutional investors:

     (1)  clients of William Blair's Investment Management Department;

     (2)  clients of William Blair's Private Investors Department;

     (3)  tax-exempt retirement plans (Profit Sharing, 401(k), Money Purchase
          Pension and Defined Benefit Plans) of William Blair and it affiliates
          and rollover accounts from those plans;

     (4)  the following investment advisory clients of William Blair and its
          investment advisory affiliates that invest at least $1 million in a
          fund: unaffiliated benefit plans, such as qualified retirement plans
          (other than individual retirement accounts and self-directed
          retirement plans); unaffiliated banks and insurance companies
          purchasing for their own accounts; and endowment funds of unaffiliated
          non-profit organizations;

     (5)  investment-only accounts for large qualified plans, with at least $50
          million in total plan assets or at least 1,000 participants;

     (6)  trust and fiduciary accounts of trust companies and bank trust
          departments providing fee-based advisory services that invest at least
          $1 million in a fund on behalf of each trust;

     (7)  investment companies managed by William Blair that invest primarily in
          other investment companies. Class I shares currently are available for
          purchase only from William Blair, principal underwriter for the funds,
          and, in the case of category 6 above, selected dealers authorized by
          William Blair.

Share certificates will not be issued unless requested in writing and may not be
available for certain types of account registrations. It is recommended that
investors not request share certificates unless needed for a specific purpose.
You cannot redeem shares by telephone or wire transfer or use the telephone
exchange privilege if share certificates have been issued. A lost or destroyed
certificate is difficult to replace and can be expensive to the shareholder (a
bond worth 2% or more of the certificate value is normally required).

                                      B-28

<PAGE>   139

INITIAL SALES CHARGE ALTERNATIVE -- Class A Shares. The public offering price of
Class A shares for purchasers choosing the initial sales charge alternative is
the net asset value plus a sales charge, as set forth below:


<TABLE>
<CAPTION>
                                                                    EQUITY FUNDS
                                                                    SALES CHARGE
                                                  ------------------------------------------------
                                                                                        ALLOWED
                                                                                      TO DEALERS
                                                       AS A              AS A            AS A
                                                    PERCENTAGE        PERCENTAGE     PERCENTAGE OF
                                                        OF              OF NET          OFFERING
              AMOUNT OF PURCHASE                  OFFERING PRICE     ASSET VALUE*       PRICE***
              ------------------                  --------------     ------------    -------------

<S>                                                    <C>               <C>             <C>
$0 - $49,999                                           5.75%             6.10%           5.00%
$50,000 - $99,999                                      4.50%             4.71%           3.75%
$100,000 - $249,999                                    3.50%             3.63%           2.75%
$250,000 - $499,999                                    2.50%             2.56%           2.00%
$500,000 - $999,999                                    2.00%             2.04%           1.75%
$1 million and over**                                  0.00%             0.00%           1.00%
</TABLE>

- ------------------

*        Rounded to the nearest one-hundredth percent.
**       Redemption of shares may be subject to a contingent deferred sales
         charge as discussed below.
***      Commission is payable by the Distributor as discussed below.


<TABLE>
<CAPTION>
                                                                      INCOME FUND
                                                                     SALES CHARGE
                                                  --------------------------------------------------
                                                                                          ALLOWED
                                                                                         TO DEALERS
                                                       AS A                AS A            AS A
                                                    PERCENTAGE          PERCENTAGE     PERCENTAGE OF
                                                        OF                OF NET          OFFERING
              AMOUNT OF PURCHASE                  OFFERING PRICE       ASSET VALUE*       PRICE***
              ------------------                  --------------       ------------    -------------

<S>                                                   <C>                 <C>             <C>
$0 - $49,999                                          2.00%               2.04%           1.75%
$50,000 - $99,999                                     2.00%               2.04%           1.75%
$100,000 - $249,999                                   1.50%               1.52%           1.25%
$250,000 - $499,999                                   1.50%               1.52%           1.25%
$500,000 - $999,999                                   1.00%               1.01%           0.75%
$1 million and over**                                    0%                  0%              0%
</TABLE>

- ------------------

*        Rounded to the nearest one-hundredth percent.
**       Redemption of shares may be subject to a contingent deferred sales
         charge as discussed below.
***      Commission is payable by the Distributor as discussed below.

Each Fund (except Ready Reserves) receives the entire net asset value of all
its Class A shares sold. The Distributor retains the sales charge on sales of
Class A shares from which it allows discounts from the applicable public
offering price to investment dealers, which discounts are uniform for all
dealers in the United States and its territories. The normal discount allowed
to dealers is set forth in the above table. Upon notice to all dealers with
whom it has sales agreements, the Distributor may allow up to the full
applicable sales charge, as shown in the above table, during periods and for
transactions specified in such notice and such reallowances may be based upon
attainment of minimum sales levels. During periods when 90% or more of the
sales charge is reallowed, such dealers may be deemed to be underwriters as
that term is defined in the Securities Act of 1933.

Class A shares of a Fund may be purchased at net asset value to the extent that
the amount invested represents the net proceeds from a redemption of shares of a
mutual fund for which William Blair or an affiliate does not serve as investment
manager ("non-William Blair Fund") provided that: (a) the investor has
previously paid either an initial sales charge in connection with the purchase
of the non-William Blair Fund shares, and (b) the purchase of Fund






                                     B-29
<PAGE>   140

shares is made within 90 days after the date of such redemption. To make such a
purchase at net asset value, the investor or the investor's dealer must, at the
time of purchase, submit a request that the purchase be processed at net asset
value pursuant to this privilege. The Distributor may in its discretion
compensate firms for sales of Class A shares under this privilege at a
commission rate of 0.50% of the amount of Class A shares purchased. The
redemption of the shares of the non-William Blair Fund is, for Federal income
tax purposes, a sale upon which a gain or loss may be realized.

Class A shares of a Fund may be purchased at net asset value by: (a) any
purchaser provided that the amount invested in such Fund or other William Blair
Mutual Funds listed under " Special Features -- Class A Shares-- Combined
Purchases" totals at least $1,000,000 including purchases of Class A shares
pursuant to the "Combined Purchases," "Letter of Intent" and "Cumulative
Discount" features described under "Special Features"; or (b) a
participant-directed qualified retirement plan described in Code Section
401(a), a participant-directed non-qualified deferred compensation plan
described in Code Section 457 or a participant-directed qualified retirement
plan described in Code Section 403(b)(7) which is not sponsored by a K-12
school district, provided in each case that such plan has not less than 200
eligible employees (the "Large Order NAV Purchase Privilege"). Redemption
within two years of shares purchased under the Large Order NAV Purchase
Privilege may be subject to a contingent deferred sales charge. See "Contingent
Deferred Sales Charge-Large Order NAV Purchase Privilege" below.

The Distributor may in its discretion compensate investment dealers or other
financial services firms in connection with the sale of Class A shares of a
Fund at net asset value in accordance with the Large Order NAV Purchase
Privilege up to the following amounts: 1.00% of the net asset value of shares
of all Funds (except the Income Fund) and sold 0.25% on the net asset value of
shares of the Income Fund sold. The commission schedule will be reset on a
calendar year basis for sales of shares pursuant to the Large Order NAV
Purchase Privilege to employer sponsored employee benefit plans using the
subaccount recordkeeping system available through William Blair. For purposes
of determining the appropriate commission percentage to be applied to a
particular sale, the Distributor will consider the cumulative amount invested
by the purchaser in a Fund and other Funds listed under "Special
Features--Class A Shares--Combined Purchases," including purchases pursuant to
the "Combined Purchases," "Letter of Intent" and "Cumulative Discount" features
referred to above. The privilege of purchasing Class A shares of a Fund at net
asset value under the Large Order NAV Purchase Privilege is not available if
another asset value purchase privilege also applies.

Class A shares of a Fund may be purchased at net asset value by persons who
purchase such shares through bank trust departments that process such trades
through an automated, integrated mutual fund clearing program provided by a
third party clearing firm.

Class A shares of a Fund may be purchased at net asset value in any amount by
certain professionals who assist in the promotion of William Blair Funds
pursuant to personal services contracts with the Distributor, for themselves or
members of their families. The Distributor in its discretion may compensate
financial services firms for sales of Class A shares under this privilege at a
commission rate of [0.50%] of the amount of Class A shares purchased.

Class A shares may be sold at a net asset value in any amount to: (a) officers,
trustees, directors, employees (including retirees) and sales representatives
of a Fund, its investment manager, it principal underwriter or certain
affiliate companies, for themselves or members of their families; (b)
registered representatives and employees of broker-dealers having selling group
agreements with the Distributor and officers, directors and employees of
service agents of the Funds, for themselves or their spouses or dependent
children; and (c) any trust, pension, profit-sharing or other benefit plan for
only such persons. Class A shares may be sold at net asset value in any amount
to selected employees (including their spouses and dependent children) of banks
and other financial services firms that provide services related to order
placement and payment to facilitate transactions in shares of the Funds on
their clients pursuant to an agreement with the Distributor or one of its
affiliates. Only those employees of such banks and other firms who as part of
their usual duties provide services related to transactions in Fund shares may
purchase Fund Class A shares at net asset value hereunder. Class A shares of a
Fund may be sold at net asset value through certain investment advisers
registered under the Investment Advisors Act of 1940 and other financial
services firms that adhere to certain standards established by the Distributor,
including a requirement that such shares be sold for the benefit of their
clients participating in an investment advisory program under which such
clients pay a fee to the Adviser or other firm for portfolio management and
other services. Such shares are sold for investment purposes and on the
condition that they will not be resold except through redemption or repurchase
by the Funds. The Funds




                                     B-30
<PAGE>   141


may also issue Class A shares at net asset value in connection with the
acquisition of the assets of or merger or consolidation with another investment
company, or to shareholders in connection with the investment or reinvestment
of income and capital gain dividends.

The sales charge scale is applicable to purchases made at one time by any
"purchaser" which includes: an individual; or an individual, his or her spouse
and children under the age of 21; or a trustee or other fiduciary of a single
trust estate or single fiduciary account; or an organization exempt from
federal income tax under Section 501(c)(3) or (13) of the code; or a pension,
profit-sharing or other employee benefit plan whether or not qualified under
Section 401 of the Code; or other organized group of persons whether
incorporated or not, provided the organization has been in existence for at
least six months and has some purpose other than the purchase of redeemable
securities of a registered investment company at a discount. In order to
qualify for a lower sales charge, all orders from an organized group will have
to be placed through a single investment dealer or other firm and identified as
originating from a qualifying purchaser.

DEFERRED SALES CHARGE ALTERNATIVE--CLASS B SHARES. Investors choosing the
deferred sales charge alternative may purchase Class B shares at net asset
value per share without any sales charge at the time of purchase. Since Class B
shares are being sold without an initial sales charge, the full amount of the
investor's purchase payment will be invested in Class B shares for his or her
account. A contingent deferred sales charge may be imposed upon redemption of
Class B shares. See "Redemption or Repurchase of Shares--Contingent Deferred
Sales Charge--Class B Shares."

The Distributor compensates firms for sales of Class B shares at the time of
sale at a commission rate of up to ____% of the amount of Class B shares
purchased. The Distributor is compensated by each Fund for services as
distributor and principal underwriter for Class B shares. See "Investment
Manager" and "Distributor."

Class B shares of a Fund will automatically convert to Class A shares of the
same fund eight years (three years for the Income Fund) after issuance on the
basis of the relative net asset value per share. The purpose of the conversion
feature is to relieve holders of Class B shares from the distribution services
fee when they have been outstanding long enough for the Distributor to have
been compensated for distribution related expenses. For purposes of conversion
to Class A shares, shares purchased through the reinvestment of dividends and
other distributions paid with respect to Class B shares in a shareholder's Fund
account will be converted to Class a shares on a pro rata basis.

PURCHASE OF CLASS C SHARES. The public offering price of the Class C shares of
a Fund (except Ready Reserves) is the next determined net asset value. No
initial sales charge is imposed. Since Class C shares are sold without an
initial sales charge, the full amount of the investor's purchase payment will
be invested in Class C shares for his or her account. A contingent deferred
sales charge may be imposed upon the redemption of Class C shares if they are
redeemed within one year of purchase. See "Contingent Deferred Sales
Charge--Class C Shares" below. The Distributor currently advances to firms the
first year distribution fee at a rate of 0.75% of the purchase price of such
shares. For periods after the first year, the Distributor currently intends to
pay firms for sales of Class C shares a distribution fee, payable quarterly, at
an annual rate of 0.75% of net assets attributable to Class C shares maintained
and serviced by the firm. The Distributor is compensated by each Fund for
services as distributor and principal underwriter for Class C shares. See
"Investment Manager and Underwriter."

PURCHASE OF CLASS R AND CLASS I SHARES. The public offering price of the Class
R and Class I shares of a Fund (except Ready Reserves) is the next determined
net asset value. No initial sales charge or contingent deferred charge is
imposed. Since Class R and Class I shares are sold without an initial sales
charge, the full amount of the investor's purchase payment will be invested in
Class R and Class I shares for his or her account.

GENERAL. Banks and other financial services firms may provide services related
to order placement and payment to facilitate transactions in shares of a Fund
for their clients, and the Distributor may pay them a transaction fee up to the
level of the discount or commission allowable or payable to dealers, as
described above. Banks are currently prohibited under the Glass-Steagall Act
from providing certain underwriting or distribution services. Banks or other
financial services firms may be subject to various state laws regarding the
services described above and may be required to register as dealers pursuant to
state law. If banking firms were prohibited from acting in any capacity or
providing any of the described services, management would consider what action,
if any, would be appropriate.




                                     B-31
<PAGE>   142

The Distributor does not believe that termination of a relationship with a bank
would result in any material adverse consequences to a Fund.

The Distributor may, from time to time, pay or allow to firms a 1% commission
on the amount of shares of the Fund sold under the following conditions: (i)
the purchase shares are held in a William Blair IRA account, (ii) the shares
are purchased as a direct "roll over" of a distribution from a qualified
retirement plan account maintained on a participant subaccount record keeping
system provided by William Blair, (iii) the registered representative placing
the trade is a member of _______, a group of persons designated by the
Distributor in acknowledgment of their dedication to the employee benefit plan
area; and (iv) the purchase is not otherwise subject to a commission.

In addition to the discounts or commissions described above, the Distributor
will, from time to time, pay or allow additional discounts, commissions or
promotional incentives, in the form of cash or other compensation, to firms
that sell shares of the Funds. Noncash compensation includes luxury merchandise
and trips to luxury resorts. In some instances, such discounts, commissions or
other incentives will be offered only to certain firms that sell or are
expected to sell during specified time periods certain minimum amounts of
shares of the Funds, or other funds underwritten by the Distributor.

Orders for the purchase of shares of a Fund will be confirmed at a price based
on the net asset value of that Fund next determined after receipt by the
Distributor of the order accompanied by payment. However, orders received by
dealers or other financial services firms prior to the determination of net
asset value (see "Net Asset Value") and received by the Distributor prior to
the close of its business day will be confirmed at a price based on the net
asset value effective on that day ("trade date"). The Funds reserve the right
to determine the net asset value more frequently than once a day if deemed
desirable. Dealers and other financial services firms are obligated to transmit
orders promptly. Collection may take significantly longer for a check drawn on
a foreign bank than for a check drawn on a domestic bank. Therefore, if an
order is accompanied by a check drawn on a foreign bank, funds must normally be
collected before shares will be purchased.

Investment dealers and other firms provide varying arrangements for their
clients to purchase and redeem the Funds' shares. Some may establish higher
minimum investment requirement than set forth above. Firms may arrange with
their clients for other investments or administrative services. Such firms may
independently establish and charge additional amounts to their clients for such
services, which charges would reduce the clients' return. Firms also may hold
the Funds' shares in nominee or street name as agent for and on behalf of their
customers. In such instances, the Funds' transfer agent will have no
information with respect to or control over the accounts of specific
shareholders. Such shareholders may obtain access to their accounts and
information about their accounts only from their firm. Certain of these firms
may receive compensation from the Funds through the Distributor for
recordkeeping and other expenses relating to these nominee accounts. In
addition, certain privileges with respect to the purchase and redemption of
shares or the reinvestment of dividends may not be available through such
firms. Some firms may participate in a program allowing them access to their
client's accounts for servicing including, without limitation, transfers of
registration and dividend payee changes; and may perform functions such as
generation of confirmation statements and reimbursement of cash dividends. Such
firms may receive compensation from the Funds through the Distributor Service
Agent for these services. This statement of additional information should be
read in connection with such firms' material regarding their fees and services.

The Funds reserve the right to withdraw all or any part of the offering made by
this statement of additional information and reject purchase orders. Also, from
time to time, each Fund may temporarily suspend the offering of any class of
its shares to new investors. During the period of such suspension, persons who
are already shareholders of such class of such Fund normally are permitted to
continue to purchase additional shares of such class and to have dividends
reinvested.

The conversion of Class B shares to Class A shares may be subject to the
continuing availability of an opinion of counsel, ruling by the Internal
Revenue Service or other assurance acceptable to each Fund to the effect that
(a) the assessment of the distribution services fee with respect to Class B
shares and not Class A shares does not result in the Fund's dividends
constituting "preferential dividends" under the Internal Revenue Code, and (b)
that the conversion of Class B shares to Class a shares doe not constitute a
taxable event under the Internal Revenue Code. The conversion of Class B shares
to Class a shares may be suspended if such assurance is not available. In that
event, no further conversion of Class B shares would occur, and shares might
continue to be subject to the






                                     B-32
<PAGE>   143


distribution services fee for an indefinite period that may extend beyond the
proposed conversion date as described herein.

The Funds have authorized certain members of the National Association of
Securities Dealers, Inc. ("NASD"), other than the Distributor to accept purchase
and redemption orders for the Funds' shares. Those brokers may also designate
other parties to accept purchase and redemption orders on the Funds' behalf.
Orders for purchase or redemption will be deemed to have been received by the
Fund when such brokers or their authorized designees accept the orders. Subject
to the terms of the contract between the Fund and the broker, ordinarily orders
will be priced as the Fund's net asset value next computed after acceptance by
such brokers or their authorized designees. Further, if purchases or redemptions
of the Fund's shares are arranged and settlement is made at an investor's
election through any other authorized NASD member, that member may, at its
discretion, charge a fee for that service. The Board of Directors of the Fund
and the Distributor each has the right to limit the amount of purchases by, and
to refuse to sell to, any person. The Board of Directors and the Distributor may
suspend or terminate the offering of shares of the Fund at any time for any
reason.


REDEMPTIONS. Suspension of Redemption or Delay in Payment. The Fund may not
suspend the right of redemption or delay payment on its shares for more than
seven days except (a) during any period when the New York Stock Exchange is
closed (other than on weekends and customary holidays); (b) when trading in the
markets that the portfolio normally utilizes is restricted or any emergency
exists as determined by the Securities and Exchange Commission, so that disposal
of the portfolio's investments or determination of its net asset value is not
reasonably practicable; or (c) for such other periods as the Securities and
Exchange Commission may permit by order for protection of the Fund's
shareholders.

SPECIAL REDEMPTIONS. Although it is the present policy of all six of the
portfolios to redeem portfolio shares in cash, if the Board of Directors
determines that a material adverse effect would be experienced by the remaining
shareholders if payment of large redemptions were made wholly in cash, the
portfolios will pay the redemption price in whole or in part by a distribution
of portfolio instruments in lieu of cash, in conformity with the applicable
rules of the Securities and Exchange Commission, taking such instruments at the
same value used to determine net asset value and selecting the instruments in
such manner as the Board of Directors may deem fair and equitable. If such a
distribution occurs, shareholders receiving instruments and selling them before
their maturity could receive less than the redemption value of such instruments
and could also incur transaction costs. The portfolios have elected to be
governed by Rule 18f-1 under the 1940 Act, pursuant to which the portfolios are
obligated to redeem portfolio shares solely in cash up to the lesser of $250,000
or 1% of the net asset value of the portfolio during any 90-day period for any
one shareholder of record.


CONTINGENT DEFERRED SALES CHARGE--LARGE ORDER NAV PURCHASE PRIVILEGE. A
contingent deferred sales charge may be imposed upon redemption of Class A
shares that are purchased under the Large Order NAV Purchase Privilege as
follows: for all Funds (except the Income Fund), 1% if they are redeemed within
one year of purchase and 0.50% if they are redeemed during the second year
after purchase and for the Income Fund, 0.25% if they are redeemed within one
year of purchase. The charge will not be imposed upon redemption of reinvested
dividends or share appreciation. The charge is applied to the value of the
shares redeemed, excluding amounts not subject to the charge. The contingent
deferred sales charge will be waived in the event of: (a) redemptions by a
participant-directed qualified retirement plan described in Code Section
401(a), a participant-directed non-qualified deferred compensation plan
described in Code Section 457 or a participant-directed qualified retirement
plan described in Code Section 403(b)(7) which is not sponsored by a K-12
school district; (b) redemptions by employer sponsored employee benefit plans
using the subaccount record keeping system made available through the
Distributor; (c) redemption of shares of a shareholder (including a registered
joint owner) who has died; (d) redemption of shares of a shareholder (including
a registered joint owner) who after purchase of the shares being redeemed
becomes totally disabled (as evidenced by a determination by the federal Social
Security Administration); (e) redemptions under a Fund's Systematic Withdrawal
Plan at a maximum of 10% per year of the net asset value of the account; and
(f) redemptions of shares whose dealer of record at the time of the investment
notifies the Distributor that the dealer waives the discretionary commission
applicable to such Large Order NAV Purchase Privilege.



CONTINGENT DEFERRED SALES CHARGE--CLASS B SHARES. A contingent deferred sales
charge may be imposed upon redemption of Class B shares. There is no such charge
upon redemption of any share appreciation or reinvested dividends on Class B
shares. The charge is applied to the value of the shares redeemed, excluding
amounts not






                                     B-33
<PAGE>   144

subject to the charge. The charge is computed at the following rates applied to
the value of the shares redeemed excluding amounts not subject to the charge.


<TABLE>
<CAPTION>
                                                 EQUITY FUNDS               INCOME FUNDS
                                              CONTINGENT DEFERRED        CONTINGENT DEFERRED
    YEAR OF REDEMPTION AFTER PURCHASE            SALES CHARGE               SALES CHARGE
    ---------------------------------            ------------               ------------

<S>                                                  <C>                       <C>
First....................................            5.00%                     2.00%
Second...................................            4.00%                     1.00%
Third....................................            3.00%                     0.00%
Fourth...................................            3.00%                     0.00%
Fifth....................................            2.00%                     0.00%
Sixth....................................            1.00%                     0.00%
Seventh..................................            0.00%                     0.00%
</TABLE>

The contingent deferred sales charge will be waived: (a) in the event of the
total disability (as evidenced by a determination by the federal Social Security
Administration) of the shareholder (including a registered joint owner)
occurring after the purchase of the shares being redeemed, (b) in the event of
the death of the shareholder (including a registered joint owner), (c) for
redemptions made pursuant to a systematic withdrawal plan (see "Special
Features--Systematic Withdrawal Plan" below), (d) for redemptions made pursuant
to any IRA systematic withdrawal based on the shareholder's life expectancy
including, but not limited to, substantially equal periodic payments described
in Internal Revenue Code Section 72(t)(2)(A)(iv) prior to age 59 1/2 and (e) for
redemptions to satisfy required minimum distributions after age 70 1/2 from an
IRA account (with the maximum amount subject to this waiver being based only
upon the shareholder's William Blair IRA accounts). The contingent deferred
sales charge will also be waived in connection with the following redemptions of
shares held by employer sponsored employee benefit plans maintained on the
subaccount record keeping system made available by the Distributor: (a)
redemptions to satisfy participant loan advances (note that loan repayments
constitute new purchases for purposes of the contingent deferred sales charge
and the conversion privilege), (b) redemptions in connection with retirement
distributions (limited at any one time to 10% of the total value of plan assets
invested in a Fund), (c) redemptions in connection with distributions qualifying
under the hardship provisions of the Internal Revenue Code and (d) redemptions
representing returns of excess contributions to such plans.

CONTINGENT DEFERRED SALES CHARGE--CLASS C SHARES. A contingent deferred sales
charge of 1% may be imposed upon redemption of Class C shares if they are
redeemed within one year of purchase. The charge will not be imposed upon
redemption of reinvested dividends or share appreciation. The charge is applied
to the value of the shares redeemed excluding amounts not subject to the
charge. The contingent deferred sales charge will be waived: (a) in the event
of the total disability (as evidenced by a determination by the federal Social
Security Administration) of the shareholder (including a registered joint
owner) occurring after the purchase of the shares being redeemed, (b) in the
event of the death of the shareholder (including a registered joint owner), (c)
for redemptions made pursuant to a systematic withdrawal plan (limited to 10%
of the net asset value of the account during the first year, see "Special
Features--Systematic Withdrawal Plan"), (d) for redemptions made pursuant to
any IRA systematic withdrawal based on the shareholder's life expectancy
including, but not limited to, substantially equal periodic payments described
in Internal Revenue Code Section 72(t)(2)(A)(iv) prior to age 59 1/2, (e) for
redemptions to satisfy required minimum distributions after age 70 1/2 from an
IRA account (with the maximum amount subject to this waiver being based only
upon the shareholder's William Blair IRA accounts), (f) for any
participant-directed redemptions of shares held by employer sponsored employee
benefit plans maintained on the subaccount record keeping system made available
by the Distributor and (g) redemption of shares by an employer sponsored
employee benefit plan that offers funds in addition to William Blair Funds and
whose dealer of record has waived the advance of the first year administrative
service and distribution fees applicable to such shares and agrees to receive
such fees quarterly.

CONTINGENT DEFERRED SALES CHARGE--GENERAL. The following example will
illustrate the operation of the contingent deferred sales charge. Assume that
an investor makes a single purchase of $10,000 of a Fund's Class B shares and
that 16 months later the value of the shares has grown by $1,000 through
reinvested dividends and by an additional $1,000 of share appreciation to a
total of $12,000. If the investor were then to redeem the entire $12,000 in
share value, the contingent deferred sales charge would be payable only with
respect to $10,000 because neither





                                     B-34
<PAGE>   145


the $1,000 of reinvested dividends nor the $1,000 of share appreciation is
subject to the charge. The charge would be at the rate of % ($. ) ----- because
it was in the second year after the purchase was made.

The rate of the contingent deferred sales charge is determined by the length of
the period of ownership. Investments are tracked on a monthly basis. The period
of ownership for this purpose begins the first day of the month in which the
order for the investment is received. For example, an investment made in
December, 1999 will be eligible for the second year's charge if redeemed on or
after December 1, 2000. In the event no specific order is requested when
redeeming shares subject to a contingent deferred sales charge, the redemption
will be made first from shares representing reinvested dividends and then from
the earliest purchase of shares. The Distributor receives any contingent
deferred sales charge directly.

SPECIAL FEATURES.

CLASS A SHARES--COMBINED PURCHASES. Each Fund's Class A shares (or the
equivalent) may be purchased at the rate applicable to the discount bracket
attained by combining concurrent investments in Class A shares of any William
Blair Fund.

CLASS A SHARES--LETTER OF INTENT. The same reduced sales charges for Class A
shares, as shown in the applicable prospectus or statement of additional
information, also apply to the aggregate amount of purchase of such Fund made by
any purchaser within a 24-month period under a written Letter of Intent
("Letter") provided by the Distributor. The Letter, which imposes no obligation
to purchase or sell additional Class A shares, provides for a price adjustment
depending upon the actual amount purchased within such period. The Letter
provides that the first purchase following execution of the Letter must be at
least 5% of the amount of the intended purchase, and that 5% of the amount of
the intended purchase normally will be held in escrow in the form of shares
pending completion of the intended purchase. If the total investments under the
Letter are less than the intended amount and thereby qualify only for a higher
sales charge than actually paid, the appropriate number of escrowed shares are
redeemed and the proceeds used toward satisfaction of the obligation to pay the
increased sales charge. The Letter for an employer sponsored employee benefit
plan maintained on the subaccount record keeping system available through the
Distributor may have special provisions regarding payment of any increased sales
charge resulting from a failure to complete the intended purchase under the
Letter. A shareholder may include the value (at the maximum offering price) of
all shares of such William Blair Funds held of record as of the initial purchase
date under the Letter as an "accumulation credit" toward the completion of the
Letter, but no price adjustment will be made on such shares. Only investments in
Class A shares are included in this privilege.

CLASS A SHARES--CUMULATIVE DISCOUNT. Class A shares of a Fund may also be
purchased at the rate applicable to the discount bracket attained by adding to
the cost of shares of a Fund being purchased, the value of all Class A shares of
the William Blair Funds (computer at the maximum offering price at the time of
purchase for which the discount is applicable) already owned by the investor.

CLASS A SHARES--AVAILABILITY OF QUANTITY DISCOUNTS. An investor or the
investor's dealer or other financial services firm must notify the Distributor
whenever a quantity discount or reduced sales charge is applicable to a
purchase. Upon such notification, the investor will receive the lowest
applicable sales charge. Quantity discounts described above may be modified or
terminated at any time.

EXCHANGE PRIVILEGE. Shareholders of Class A, Class B, Class C , Class R and
Class I shares may exchange their shares for shares of the corresponding class
of other William Blair Funds in accordance with the provisions below. In
addition shares of any class of a Fund may be exchanged for shares of Ready
Reserves Fund and shares of Ready Reserves Fund may be exchanged for shares of
the Funds in accordance with the provisions below.

Class A Shares. Class A shares of the William Blair Funds may be exchanged for
each other at their relative net asset values.




                                     B-35
<PAGE>   146


Class A shares of a Fund purchased under the Large Order NAV Purchase Privilege
may be exchanged for Class A shares of another William Blair Fund under the
exchange privilege described above without paying any contingent deferred sales
charge at the time of exchange. If the Class A shares received on exchange are
redeemed thereafter, a contingent deferred sales charge may be imposed in
accordance with the foregoing requirements provided that the shares redeemed
will retain their original cost and purchase date for purposes of the contingent
deferred sales charge.

Class B Shares. Class B shares of a Fund may be exchanged for each other at
their relative net asset values. Class B shares may be exchanged without a
contingent deferred sales charge being imposed at the time of exchange. For
purposes of the contingent deferred sales charge that may be imposed upon the
redemption of the Class B shares received on exchange, amounts exchanged retain
their original cost and purchase date.

Class C Shares. Class C shares of a Fund may be exchanged for each other at
their relative net asset values. Class C shares may be exchanged without a
contingent deferred sales charge being imposed at the time of exchange. For
determining whether there is a contingent deferred sales charge that may be
imposed upon the redemption of the Class C shares received, by exchange, they
retain the cost and purchase date of the shares that were originally purchased
and exchanged.

Class R Shares and Class I Shares. Class R and I Shares of a Fund may be
exchanged for each other at their relative net asset values.

Class A Shares, Class B Shares, Class C Shares, Class R Shares and Class I
Shares. Class A, B, C, R and I shares may be exchanged at the same day's
relative net asset values for shares of Ready Reserves but will be subject to
any applicable contingent deferred sales charges. Shares of Ready Reserves may
be exchanged at the same day's relative net asset values for shares of any class
of a Fund subject to all applicable sales loads.

General. Shares of a William Blair Fund with a value in excess of $1,000,000
acquired by exchange from another William Blair Fund may not be exchanged
thereafter until they have been owned for 15 days (the "15-Day Hold Policy").
For purposes of determining whether the 15-Day Hold Policy applies to a
particular exchange, the value of the shares to be exchanged shall be computed
by aggregating the value of shares being exchanged for all accounts under
common control, discretion or advice, including without limitation accounts
administered by a financial services firm offering market timing, asset
allocation or similar services. The total value of shares being exchanged must
at least equal the minimum investment requirement of the Fund into which they
are being exchanged. Exchanges are made based on relative dollar values of the
shares involved in the exchange. There is no service fee for an exchange;
however, dealers or other firms may charge for their services in effecting
exchange transactions. Exchanges will be effected by redemption of shares of
the fund held and purchase of shares of the other Fund. For federal income tax
purposes, any such exchange constitutes a sale upon which a gain or loss may be
realized, depending upon whether the value of the shares being exchanged is
more or less than the shareholder's adjusted cost basis of such shares.
Shareholders interested in exercising the exchange privilege may obtain
prospectuses of the other funds from dealers, other firms or the Distributor.
Exchanges may be accomplished by a written request to William Blair, __________,
or by telephone if the shareholder has given authorization. Once the
authorization is on file, the Distributor will honor requests by telephone at
__________________, subject to the limitations on liability under "Purchase,
Repurchase and Redemption of Shares--General." Any share certificates must be
deposited prior to any exchange of such shares. During periods when it is
difficult to contact the Distributor by telephone, it may be difficult to use
the telephone exchange privilege. The exchange privilege is not a right and may
be suspended, terminated or modified at any time. Exchanges may only be made for
the funds that are available for sale in the shareholder's state of residence.


                            GENERAL FUND INFORMATION

DETERMINATION OF NET ASSET VALUE. For each portfolio, net asset value is not
determined on the days that the New York Stock Exchange is closed, which include
the observance of New Year's Day, Dr. Martin Luther King Jr.'s Birthday,
President's Day, Good Friday, Memorial Day, Independence Day, Labor Day,
Thanksgiving Day and Christmas Day. In addition, the net asset value for the
Ready Reserves Fund is not calculated on the observance of





                                     B-36
<PAGE>   147

Columbus Day and Veteran's Day. Net asset value is not required to be computed
on a day when no orders to purchase shares were received and no shares were
tendered for redemption.

As mentioned in the prospectus, the Ready Reserves Fund values its portfolio
instruments at amortized cost in accordance with Rule 2a-7 under the 1940 Act,
which means that they are valued at their acquisition cost (as adjusted for
amortization of premium or discount), rather than at current market value. This
involves initially valuing an instrument at its cost and thereafter assuming a
constant amortization to maturity of any discount or premium, regardless of the
impact of fluctuating interest rates on the market value of the instrument.
While this method provides certainty in valuation, it may result in periods
during which value, as determined by amortized cost, is higher or lower than the
price the portfolio would receive if it sold the instrument. Calculations are
made to compare the value of the portfolio's investments valued at amortized
cost with market values. Market valuations are obtained by using actual
quotations provided by market makers, estimates of market value or values
obtained from yield data relating to classes of money market instruments
published by reputable sources at the bid price for such securities.

If a deviation of one-half of one percent or more were to occur between the net
asset value per share calculated by reference to market values and the
portfolio's $1.00 per share net asset value, or if there were any other
deviation that the Board of Directors determined would result in a material
dilution to shareholders or purchasers, the Board of Directors would promptly
consider what action, if any, should be initiated. If the portfolio's net asset
value per share (computed using market values) declined, or was expected to
decline, below $1.00 (computed using amortized cost), the Board of Directors of
the Fund might temporarily reduce or suspend dividend payments in an effort to
maintain the net asset value at $1.00 per share. As a result of such reduction
or suspension of dividends or other action by the Board of Directors, an
investor would receive less income during a given period than if such a
reduction or suspension had not taken place. Such action could result in
investors receiving no dividends for the period during which they held shares
and receiving, upon redemption, a price per share lower than that which they
paid. On the other hand, if the portfolio's net asset value per share (computed
using market values) were to increase, or were anticipated to increase, above
$1.00 (computed using amortized cost), the Board of Directors of the Fund might
supplement dividends in an effort to maintain the net asset value at $1.00 per
share.

The Ready Reserves Fund has never had a deviation of one-half of one percent or
more between its net asset value per share calculated by reference to market
values and its $1.00 per share net asset value; therefore, no Board actions of
the type described above have been taken. To use the amortized cost method of
valuation, the portfolio is limited to investing in instruments that the Board
of Directors has determined present minimal credit risks and that are within
certain rating categories of a nationally recognized statistical rating
organization.

PERFORMANCE.

HISTORICAL PERFORMANCE

In general. The historical performance or return of the Growth Fund, the Value
Discovery Fund, the International Growth Fund, the Emerging Markets Growth Fund
and the Income Fund may be shown in the form of "average annual total return"
and "total return" figures. The Income Fund's and Ready Reserves Fund's
historical performance or return may also be shown in the form of "yield
figures." These various measures of performance are described below.

Average annual total return and total return measure both the net investment
income generated by and the effect of any realized and unrealized appreciation
or depreciation of, the underlying investments of the portfolio, assuming the
reinvestment of all dividends during the period. Average annual total return
figures represent the average annual percentage change over the period in
question. Total returns represent the aggregate percentage or dollar value
change over the period in question. Yield is a measure of the net investment
income per share earned over a specified period, expressed as a percentage of
the net asset value. Yield is an annualized figure, which means that it assumes
that a portfolio generates the same level of net investment income over a
one-year period.

The performance quotations for all of the portfolios are based upon historical
results and are not necessarily representative of future performance. Returns
and net asset value will fluctuate. The portfolios' performance depends upon
general market conditions, operating expenses and the performance of the
investment manager. Any





                                     B-37
<PAGE>   148

additional fees charged by a dealer or other financial services firm would
reduce the returns described in this section.

In addition, from time to time the adviser has voluntarily absorbed certain
operating expenses of certain of the portfolios. For the Income Fund, the
Adviser has voluntarily waived certain advisory management fees for the fiscal
years from 1990 to 1993 and to the extent described under "Management of the
Fund--Investment Adviser and Distributor." For the Value Discovery Fund, the
Adviser has voluntarily waived certain advisory fees from December 23, 1996
(Commencement of Operations) to December 31, 1997 and to the extent described
under "Management of the Fund -- Investment Adviser and Distributor." For the
Emerging Markets Growth Fund, the Adviser is currently voluntarily waiving
certain advisory management fees. Without such waiver, the performance results
noted above for these portfolios would have been lower.

Average annual total return. The portfolios' average annual total return is
computed in accordance with a standardized method prescribed by rules of the
Securities and Exchange Commission. The average annual total return for a
specific period is found by first taking a hypothetical $1,000 investment
("initial investment") in a portfolio's shares on the first day of the period
and computing the "redeemable value" of that investment at the end of the
period. The redeemable value is then divided by the initial investment and this
quotient is taken to the nth root (n representing the number of years in the
period) and 1 is subtracted from the result, which is then expressed as a
percentage. This calculation assumes that all income dividends and capital gains
distributions by the portfolio have been reinvested at net asset value on the
reinvestment dates during the period.

The average annual total return for the Funds for the one-, five- and ten-year
periods, or, if less, from commencement of operations through December 31, 1998
are as follows:


<TABLE>
<CAPTION>
                                                                                     10-YEAR OR
                                                       1-YEAR       5-YEAR          LIFE OF FUND
                                                       ------       ------          ------------

<S>                                                    <C>          <C>                <C>
Growth Fund                                            27.15        19.87              18.96
Value Discovery Fund (1)                                0.66           --              15.91
International Growth Fund (2)                          11.46         7.37              11.10
Emerging Markets Growth Fund (3)                          --           --             (23.70)
Income Fund (4)                                         7.07         6.22               7.90
</TABLE>

- ------------------

(1) Commenced operations on December 23, 1996.
(2) Commenced operations on October 1, 1992.
(3) Commenced operations on May 1, 1998.
(4) Commenced operations on September 25, 1990.

Total return. Total return performance for a specific period is calculated by
first taking an investment (assumed below to be $10,000) ("initial investment")
in a portfolio's shares on the first day of the period and computing the
"ending value" of that investment at the end of the period. The total return
percentage is then determined by subtracting the initial investment from the
ending value, dividing the remainder by the initial investment and expressing
the result as a percentage. This calculation assumes that all income and
capital gains dividends by the portfolio have been reinvested at net asset
value on the reinvestment dates during the period. Total return may also be
shown as the increased dollar value of the hypothetical investment over the
period.




                                     B-38
<PAGE>   149

The total return for the Funds for the one-, five- and ten-year periods, or, if
less, from commencement of operations through December 31, 1998 are as follows:


<TABLE>
<CAPTION>
                                                                                       10-YEAR OR
                                                           1-YEAR      5-YEAR          LIFE OF FUND
                                                           ------      ------          ------------

<S>                                                         <C>        <C>               <C>
Growth Fund                                                 27.15      147.51            467.73
Value Discovery Fund (1)                                     0.66          --             34.34
International Growth Fund (2)                               11.46       42.69             93.12
Emerging Markets Growth Fund (3)                               --          --            (23.70)
Income Fund (4)                                              7.07       35.21             87.25
</TABLE>

- ------------------

(1)   Commenced operations on December 23, 1996.
(2)   Commenced operations on October 1, 1992.
(3)   Commenced operations on May 1, 1998.
(4)   Commenced operations on September 25, 1990.

Yield. Like the portfolios' average annual total return, the yield for the
Income Fund portfolio is computed in accordance with a standardized method
prescribed by rules of the Securities and Exchange Commission. The yield is
computed by dividing the net investment income per share earned during a
specific one-month or 30-day period by the offering price per share on the last
day of that period according to the following formula:

                        YIELD = 2[(((a-b)/cd)+1)(6) - 1]

Where:            a =      dividends and interest earned during the period
                  b =      expenses accrued for the period (net of
                           reimbursements)
                  c =      the average daily number of shares outstanding
                           during the period entitled to receive dividends
                  d =      the offering price (net asset value) per share on
                           the last day of the period

The Income Fund's current yield for the 30-day period ended December 31, 1998
was 5.72%. Semiannual compounding is assumed.

In computing the foregoing yield, the portfolio follows certain standardized
accounting practices specified by Securities and Exchange Commission rules.
These practices are not necessarily consistent with those that the portfolio
uses to prepare its annual and interim financial statements in accordance with
generally accepted accounting principles.

From time to time, the Fund may include in its sales literature and shareholder
reports a quotation of the current "distribution rate" for the Income Fund.
Distribution rate is simply a measure of the level of income and short-term
capital gain dividends distributed for a specified period. It differs from
yield, which is a measure of the income actually earned by the Income Fund's
investments and from total return, which is a measure of the income actually
earned by, plus the effect of any realized or unrealized appreciation or
depreciation of, such investments during the period. Distribution rate,
therefore, is not intended to be a complete measure of performance. Distribution
rate may sometimes be greater than yield since, for instance, it may include
short-term gains (which may be nonrecurring) and may not include the effect of
amortization of bond premiums.

The Ready Reserves Fund's yield quotations as they may appear in advertising
and sales materials also are calculated by a standard method prescribed by
rules of the Securities and Exchange Commission. Under that method, the current
yield quotation is annualized based on a seven-day period and computed as
follows: the portfolio's net investment income per share (accrued interest on
portfolio securities, plus or minus amortized purchase discount or premium,
less accrued expenses) is divided by the price per share (expected to remain
constant at $1.00) during the period ("base period return") and the result is
divided by seven and multiplied by 365 and the current yield figure is carried
to the nearest one-hundredth of one percent. Realized capital gains or losses
and unrealized appreciation or depreciation of investments are not included in
the calculation. The effective yield is





                                     B-39
<PAGE>   150

determined by taking the base period return and calculating the effect of
assumed compounding according to the following formula:

                  YIELD = [(BASE PERIOD RETURN +1)(365/7)] - 1

The Ready Reserves Fund's effective yield is calculated similarly to its current
yield, except that the net investment income earned is assumed to be compounded
when annualized. The Ready Reserves Fund effective yield will be slightly higher
than its current yield due to compounding.

The Ready Reserves Fund's current yield for the seven-day period ended December
31, 1998 was 4.58%. The Ready Reserves Fund's effective yield for the same
period was 4.68%.

The Ready Reserves Fund's yield fluctuates and the publication of an annualized
yield quotation is not a representation as to what an investment in the
portfolio will actually yield for any given future period. Actual yields will
depend not only on changes in interest rates on money market instruments during
the period the investment in the portfolio is held, but also on such matters as
any realized gains and losses and changes in portfolio expenses.

COMPARISON OF FUND PERFORMANCE TO MARKET INDICES

From time to time, in marketing and other Fund literature, each portfolio's
performance may be compared to the performance of other mutual funds in general
or to the performance of particular types of mutual funds with similar goals, as
tracked by independent organizations. Such market comparisons are set forth
briefly below.

From time to time, the portfolios' performance may be compared to that of
various unmanaged stock indices such as the Standard & Poor's 500 Stock Index,
NASDAQ, Value Line and Russell 1000, 2000 and 3000. The portfolios' performance
may also be compared to the performance of other growth mutual funds or mutual
fund indices as reported by CDA Investment Technologies, Inc. ("CDA"), Lipper
Analytical Services, Inc. ("Lipper") or Morningstar, Inc.
("Morningstar").

         o        CDA: CDA is a widely recognized independent mutual fund
                  reporting service that is based upon changes in net asset
                  value with all dividends reinvested.

         o        LIPPER: Lipper is a widely used independent research firm that
                  ranks mutual funds' overall performance, investment objectives
                  and assets. Lipper performance figures are based on changes in
                  net asset value, with all income and capital gain dividends
                  assumed to be reinvested. Lipper's calculations do not include
                  the effect of any sales charges imposed by other funds. Lipper
                  also issues a monthly yield analysis for fixed- income funds.

         o        MORNINGSTAR: Morningstar rates funds on the basis of
                  historical risk and total return. Morningstar's ratings range
                  from five stars (highest) to one star (lowest) and represent
                  Morningstar's assessment of the historical risk level and
                  total return of a fund as a weighted average for three-, five-
                  and ten-year periods. Ratings are not absolute and do not
                  represent future results.

The portfolios may also compare their performance with that of indices, such as
the Consumer Price Index or the Lehman Intermediate Government/Corporate Bond
Index. The Lehman bond index is unmanaged and does not adjust for taxes payable
on interest or dividends. When assessing a portfolio's performance as compared
to that of any of these indices, it is important to note the differences and
similarities between the investments that the portfolio may purchase and the
investments measured by the applicable indices.

         o        CONSUMER PRICE INDEX: The Consumer Price Index is generally
                  considered to be a measure of inflation.


         o        LEHMAN GOVERNMENT/CORPORATE INTERMEDIATE BOND INDEX: This
                  index generally represents the performance of intermediate
                  government and investment grade corporate debt securities
                  under various market conditions.







                                     B-40
<PAGE>   151

Bank product performance may be based upon, among other things, the Bank Rate
Monitor National Index or various certificates of deposit indices. Performance
of U.S. Treasury obligations may be based upon, among other things, various U.S.
treasury bill indices. Certain of these alternative investments may offer fixed
rates of return and guaranteed principal and may be insured. Money market fund
performance may be based upon, among other things, the IBC/Donoghue's Money Fund
Average (All Taxable). Investors may also want to compare the historical returns
of various investments, performance indexes of those investments or economic
indicators, including but not limited to stocks, bonds, certificates of deposit,
money market funds and U.S. Treasury obligations and the rate of inflation.

Comparative performance information other than that listed above may be used
from time to time in advertising the International Growth Fund and the Emerging
Markets Growth Fund, including data from Micropal Ltd., an independent fund
reporting service, and independent unmanaged indices. For the International
Growth Fund indices include the Morgan Stanley Capital International's Europe,
Australia and the Far East (EAFE) Index or Morgan Stanley Capital
International's All Country World (Free) Except United States (ACWFxUS) Index.
For the Emerging Markets Growth Fund such indices include the MSCI Emerging
Markets (free) Index.

In addition, the portfolios may quote information from industry or financial
publications of general U.S. or international interest, such as information from
Morningstar, the Wall Street Journal, Money Magazine, Forbes, Barron's, Fortune,
the Chicago Tribune, USA Today, Institutional Investor and Registered
Representative.

TAX STATUS. Each series (portfolio) of the Fund is treated as a separate entity
for accounting and tax purposes. The Fund has qualified and elected to be
treated as a "regulated investment company" under Subchapter M of the Internal
Revenue Code (the "Code") and intends to continue to so qualify in the future.
As such, and by complying with the applicable provisions of the Code regarding
the sources of its income, the timing of its distributions and the
diversification of its assets, the Fund will not be subject to Federal income
tax on its taxable income (including net short-term and long-term capital gains)
that is distributed to shareholders in accordance with the timing requirements
of the Code.

Each portfolio intends to declare and make distributions during the calendar
year of an amount sufficient to prevent imposition of a 4% nondeductible Federal
excise tax. The required distribution generally is the sum of 98% of a
portfolio's net investment income for the calendar year plus 98% of its net
capital gain income for the one-year period ending October 31, plus the sum of
any undistributed net investment income and capital gain net income from the
prior year, less any over-distribution from the prior year.

The Fund is required to withhold Federal income tax at the rate of 31% (commonly
called "backup withholding") from taxable distributions to shareholders that do
not provide the Fund with a taxpayer identification (social security) number or
in other circumstances where shareholders have failed to comply with Internal
Revenue Service regulations.

Special tax provisions may accelerate or defer recognition of certain gains or
losses, change the character of certain gains or losses or alter the holding
periods of certain of a portfolio's securities. Specifically, the mark-to-market
rules of the Code may require a portfolio to recognize unrealized gains and
losses on certain forward contracts, futures and foreign currency futures held
by a portfolio at the end of the Fund's fiscal year. Under these provisions, 60%
of any capital gain net income or loss recognized will generally be treated as
long-term and 40% as short-term. Although certain foreign currency forward
contracts and foreign currency futures contracts are marked-to-market, any gain
or loss related to foreign currency fluctuations is generally treated as
ordinary income under Section 988 of the Code (see below). In addition, the
straddle rules of the Code require deferral of certain losses realized on
positions of a straddle to the extent that the portfolio has unrealized gains in
offsetting positions at year end. The portfolios have elected to mark-to-market
their investments in passive foreign investment companies for Federal income tax
purposes.

Foreign exchange gains and losses realized by the Fund in connection with
certain transactions that involve foreign currency-denominated debt securities,
certain foreign currency options, foreign currency forward contracts, foreign
currencies or payables or receivables denominated in a foreign currency are
subject to Section 988 of the Code, which generally causes such gains and
losses to be treated as ordinary income and losses and may affect the amount,
timing and character of distributions to shareholders. For example, if a
portfolio sold a foreign stock or bond and





                                     B-41
<PAGE>   152

part of the gain or loss on the sale was attributable to an increase or
decrease in the value of a foreign currency, then the currency gain or loss may
be treated as ordinary income or loss. If such transactions result in higher
net ordinary income, the dividends paid by the portfolio will be increased; if
such transactions result in lower net ordinary income, a portion of dividends
paid could be classified as a return of capital.

The International Growth Fund and Emerging Markets Growth Fund may qualify for
and make an election permitted under the "pass through" provisions of Section
853 of the Code, which allows a regulated investment company to elect to have
its foreign tax credit taken by its shareholders instead of on its own tax
return. To be eligible for this credit, more than 50% of the value of the Fund's
total assets at the close of its taxable year must consist of stock or other
securities in foreign corporations, and the Fund must have distributed at least
90% of its taxable income.

If the Fund makes this election, it may not take any foreign tax credit and may
not take a deduction for foreign taxes paid. However, the Fund is allowed to
include the amount of foreign taxes paid in a taxable year in its dividends paid
deduction. Each shareholder would then include in his gross income, and treat as
paid by him, his proportionate share of the foreign taxes paid by the Fund.

If the U.S. government were to impose any restrictions, through taxation or
other means, on foreign investments by U.S. investors such as those to be made
through the portfolio, the Board of Directors of the Fund will promptly review
the policies of the International Growth Fund to determine whether significant
changes in its investments are appropriate.

Non-U.S. investors not engaged in a U.S. trade or business with which their
investment in the Fund is effectively connected will be subject to U.S. Federal
income tax treatment that is different from that described above and in the
prospectus. Such investors may be subject to nonresident alien withholding tax
at the rate of 30% (or a lower rate under an applicable tax treaty) on amounts
treated as ordinary dividends from the Fund, unless an effective IRS Form W-8 or
authorized substitute for Form W-8 is on file, and to 31% backup withholding on
certain other payments from the Fund. Non-U.S. investors should consult their
tax advisers regarding such treatment and the application of foreign taxes to an
investment in the Fund.

RETIREMENT PLANS. The Fund offers a variety of retirement investment programs
whereby contributions are invested in shares of the Fund's portfolios and any
income dividends or capital gain distributions are reinvested in additional full
and fractional shares of the Fund.

Individual Retirement Accounts. One of the tax-deferred retirement plan accounts
that may hold Fund shares is an Individual Retirement Account ("IRA"). There are
three kinds of IRAs that an individual may establish: traditional IRAs, Roth
IRAs and education IRAs. With a traditional IRA, an individual may be able to
make a deductible contribution of up to $2,000 or, if less, the amount of the
individual's earned income for any taxable year prior to the year the individual
reaches age 70 1/2 if neither the individual nor his or her spouse is an active
participant in an employer's retirement plan. An individual who is (or who has a
spouse who is) an active participant in an employer retirement plan may be
eligible to make deductible IRA contributions; the amount, if any, of IRA
contributions that are deductible by such an individual is determined by the
individual's (and spouse's, if applicable) adjusted gross income for the year.
Even if an individual is not permitted to make a deductible contribution to an
IRA for a taxable year, however, the individual nonetheless may make
nondeductible contributions up to $2,000, or 100% of earned income if less, for
that year. A spouse also may contribute up to $2,000, as long as the spouses'
joint earned income is at least $4,000. There are special rules for determining
how withdrawals are to be taxed if an IRA contains both deductible and
nondeductible amounts. In general, a proportionate amount of each withdrawal
will be deemed to be made from nondeductible contributions; amounts treated as a
return of nondeductible contributions will not be taxable. Lump sum
distributions from another qualified retirement plan may be rolled over into a
traditional IRA also.

With a Roth IRA, an individual may make only nondeductible contributions;
contributions can be made of up to $2,000 or, if less, the amount of the
individual's earned income for any taxable year, but only if the individual's
(and spouse's, if applicable) adjusted gross income for the year is less than
$95,000 for single individuals or $150,000 for married individuals. The maximum
contribution amount phases out and falls to zero between $95,000 and $110,000
for single persons and between $150,000 and $160,000 for married persons.
Contributions to a Roth





                                     B-42
<PAGE>   153

IRA may be made even after the individual attains age 70 1/2. Distributions
from a Roth IRA that satisfy certain requirements will not be taxable when
taken; other distributions of earnings will be taxable. An individual with
adjusted gross income of $100,000 or less generally may elect to roll over
amounts from a traditional IRA to a Roth IRA. The full taxable amount held in
the traditional IRA that is rolled over to a Roth IRA will be taxable in the
year of the rollover, except rollovers made in 1998, which may be included in
taxable income over a four-year period.

An education IRA provides a method for saving for the higher education expenses
of a child; it is not designed for retirement savings. Generally, amounts held
in an education IRA may be used to pay for qualified higher education expenses
at an eligible (post-secondary) educational institution. An individual may
contribute to an education IRA for the benefit of a child under 18 years old if
the individual's income does not exceed certain limits. The maximum contribution
for the benefit of any one child is $500 per year. Contributions are not
deductible, but earnings accumulate tax-free until withdrawal, and withdrawals
used to pay qualified higher education expenses of the beneficiary (or
transferred to an education IRA of a qualified family member) will not be
taxable. Other withdrawals will be subject to tax.

Please call the Fund to obtain information regarding the establishment of IRAs.
An IRA plan custodian may charge fees in connection with establishing and
maintaining the IRA. An investor should consult with a competent tax adviser for
specific advice concerning his or her tax status and the possible benefits of
establishing one or more IRAs. The description above is only very general; there
are numerous other rules applicable to these plans to be considered before
establishing one.

Shareholders should consult their tax advisers about the application of the
provisions of tax law in light of their particular tax situations.

Simplified Employee Pension Plans. An employer may establish a SEP plan under
which the employer makes contributions to all eligible employees' IRAs. Any
portfolio's shares may be used for this purpose.

Qualified Retirement Plans. A corporation, partnership or sole proprietorship
may establish a qualified money purchase pension and profit sharing plan and
make contributions for each participant up to the lesser of 25% of each
participant's gross compensation or $30,000. Such contributions may be made by
the employer and, if certain conditions are met, participants may also make
nondeductible voluntary contributions.

Under the Code, an investor has at least seven days in which to revoke an IRA
after receiving certain explanatory information about the plan. Individuals who
have received distributions from certain qualified plans may roll over all or
part of such distributions into an IRA, which will defer taxes on the
distributions and shelter investment earnings. Trustees of qualified retirement
plans and 403(b)(7) accounts are required by law to withhold 20% of the taxable
portion of any distribution that is eligible to be "rolled over." The 20%
withholding requirement, however, does not apply to distributions from IRAs or
any part of a distribution that is transferred directly to another qualified
retirement plan, 403(b)(7) account or IRA. Shareholders are advised to consult
with a tax professional regarding this requirement.

INDEPENDENT AUDITORS. The Fund's independent auditors are Ernst & Young LLP,
Sears Tower, 233 South Wacker Drive, Chicago, Illinois 60606. Ernst & Young
audits and reports upon the Fund's annual financial statements, reviews certain
regulatory reports, prepares the Fund's Federal and state tax returns and
performs other professional accounting, auditing, tax and advisory services when
engaged to do so by the Fund.

LEGAL COUNSEL. Vedder, Price, Kaufman & Kammholz, 222 North LaSalle Street,
Chicago, Illinois 60601, is the Fund's Counsel.

CUSTODIAN. The Fund's custodian, Investors Bank and Trust Company, 200 Clarendon
Street, Boston, Massachusetts 02117, has custody of all securities and cash of
the Fund and attends to the collection of principal and income and payment for
and collection of proceeds of securities bought and sold by the Fund. The
custodian for IRAs may be State Street Bank and Trust Company, 225 Franklin
Street, Boston, Massachusetts 02110.

TRANSFER AGENT SERVICES. State Street Bank and Trust Company ("State Street"),
225 Franklin Street, Boston, Massachusetts 02110, is the Fund's transfer agent
and dividend-paying agent. State Street, as the shareholder




                                     B-43
<PAGE>   154

service agent, provides certain bookkeeping, data processing and administrative
services pertaining to the maintenance of shareholder accounts.

REPORTS TO SHAREHOLDERS. Shareholders will receive annual audited financial
statements and semi-annual unaudited financial statements.

                               SHAREHOLDER RIGHTS

All shares of each portfolio have equal rights with respect to dividends, assets
and liquidation of a portfolio and equal, noncumulative voting rights.
Noncumulative voting rights allow the holder or holders of a majority of shares,
voting together for the election of directors, to elect all the directors. All
shares of each portfolio will be voted in the aggregate, except when a separate
vote by portfolio is required under the 1940 Act. Shares are fully paid and
nonassessable when issued, are transferable without restriction and have no
preemptive or conversion rights.

Under Maryland law, the Fund generally is not required to hold annual
shareholders' meetings. Upon the written request of ten or more shareholders
that have held Fund shares for at least six months in an amount equal to the
lesser of 1% of the outstanding shares or $25,000, the Fund will either
disseminate appropriate materials (at the expense of the requesting
shareholders) or provide such shareholders access to a list of names and
addresses of all shareholders of record. The written notice must state that the
shareholders making such request wish to communicate with the other shareholders
to obtain the signatures necessary to demand a meeting to consider removal of a
director. The Fund will hold shareholders' meetings when requested to do so in
writing by one or more shareholders collectively holding at least 10% of the
shares entitled to vote or when determined by the Board of Directors in their
discretion. Shareholders' meetings also will be held in connection with the
following matters: (1) the election or removal of directors, if a meeting is
called for such purpose; (2) the adoption of any contract for which shareholder
approval is required by the Act; (3) any termination of the Fund; (4) any
amendment of the articles of incorporation; and (5) such additional matters as
may be required by law, the articles of incorporation, the by-laws of the Fund
or any registration of the Fund with the Securities and Exchange Commission or
any state, or that the directors may consider necessary or desirable, such as
changes in fundamental investment objectives, policies or restrictions.

The Fund's directors serve until the next meeting of shareholders, if any,
called for the purpose of electing directors and until the election and
qualification of their successors or until a director sooner dies, resigns,
retires, or is removed by a majority vote of the shares entitled to vote or by a
majority of the directors. In accordance with the Act, the Fund will hold a
shareholder meeting for the election of directors at such time that (1) less
than a majority of the directors has been elected by the shareholders and (2)
if, as a result of a vacancy in the Board of Directors, less than two-thirds of
the directors have been elected by the shareholders. A director may be removed
from office by a vote of the holders of a majority of the outstanding shares
entitled to vote.

                   VALUE DISCOVERY FUND--INVESTMENT CRITERIA

The Value Discovery Fund's investment objective is to seek long-term capital
appreciation. The portfolio pursues its objective by investing with a value
discipline primarily in the equity securities of small companies. In selecting
companies for investment, the Adviser evaluates the extent to which a company
meets the investment criteria set forth below. The weight given to a particular
investment criterion will depend upon the circumstances, and some portfolio
holdings may not meet all of the following criteria:

         Material Price/Value Disparity--whether the company's current market
         value reflects a material discount from the Adviser's estimate of the
         company's intrinsic value. In determining a company's intrinsic value,
         the Adviser generally will assess whether a company's share price
         appears to be inexpensive relative to any of the following: sales,
         projected earnings, projected cash flow, discounted cash flow, asset
         values and liquidation value. The discount of the market value from
         the intrinsic value is considered material when it provides an
         adequate return opportunity compared to alternative small company
         investments. The Adviser believes that the short-term market
         assessment of a company's value can differ materially from a long-term
         perspective. Therefore, price/value disparities can result from
         particular industries and companies





                                     B-44
<PAGE>   155

         currently being in disfavor in the market. As the reasons for market
         disfavor dissipate, a market reassessment can result in price
         appreciation. However, there is no guarantee that this will result in
         market appreciation for a company.

         Probable Expansion in Profitability--whether the company has a
         reasonable expectation of improving its level of profitability over a
         three-year investment horizon. The Adviser believes an expansion in
         profit margins generally results in improved market valuation.
         Therefore, the Adviser will look for companies that it believes have
         the potential for normal, sustainable levels of profitability greater
         than their current levels. Factors used to assess the normal level of
         future profitability for a company include industry profit levels and
         competitiveness and the company's competitive advantages and business
         strategy.

         Skilled and Committed Management--whether the company has a capable and
         skilled management team and a clearly articulated and logical business
         strategy with a reasonable probability of successful execution.
         Generally, this determination will be made through due diligence with
         management, which often includes on-site meetings. Factors used to
         assess management's ability to execute its business strategy include
         tangible evidence of prior business success and management's level of
         financial commitment to the company through equity ownership.

         Strong Capital Structure--whether the company has a relatively simple,
         clean financial structure without excessive use of financial leverage.
         In addition, the company should adhere to conservative and
         straightforward accounting practices.

         Positive Catalyst--the likelihood that the company will undergo a
         positive corporate change within a three-year investment horizon.
         Examples of positive corporate changes may include: successful
         execution of its business plan, acquisitions, mergers, spin-offs,
         divestitures, new products and management additions or changes. The
         portfolio seeks to invest in companies before a positive catalyst
         becomes apparent to the market.

                                  FUND HISTORY

The Fund was organized as a Maryland corporation on September 22, 1987 under the
name of William Blair Ready Reserves, Inc. On April 30, 1991, a reorganization
of the Fund and Growth Industry Shares, Inc., a Maryland corporation, occurred
such that Growth Industry Shares, Inc. was reorganized into a separate portfolio
of the Fund, now the Growth Fund portfolio, and the Fund changed its name to
William Blair Mutual Funds, Inc. Presently, the Fund is offering shares of the
six portfolios described in the prospectus. The Board of Directors of the Fund
may, however, establish additional portfolios with different investment
objectives, policies and restrictions in the future.

                       FINANCIAL INFORMATION OF THE FUND

The Fund's audited financial statements, including the notes thereto, contained
in the Fund's annual reports to shareholders for the period ended December 31,
1998, are incorporated herein by reference. Additional copies of the reports to
shareholders may be obtained without charge by writing or calling the Fund.



                                     B-45
<PAGE>   156




                                   APPENDIX A

                    DESCRIPTION OF MONEY MARKET INSTRUMENTS

The following information includes a description of certain money market
instruments in which the Ready Reserves Fund portfolio may invest to the extent
consistent with its investment objective.

UNITED STATES GOVERNMENT SECURITIES. These include marketable securities issued
by the United States Treasury, which consist of bills, notes and bonds. Such
securities are direct obligations of the United States government and are backed
by the full faith and credit of the United States. They differ mainly in the
length of their maturity. Treasury bills, the most frequently issued marketable
government security, have a maturity of up to one year and are issued on a
discount basis.

GOVERNMENT AGENCY SECURITIES. These include debt securities issued by
government-sponsored enterprises, federal agencies or instrumentalities and
international institutions. Such securities are not direct obligations of the
U.S. Treasury but involve some government sponsorship or guarantees. Different
instruments have different degrees of government backing. For example,
securities issued by the Federal National Mortgage Association are supported by
the agency's right to borrow money from the U.S. Treasury under certain
circumstances. Securities issued by the Student Loan Marketing Association are
supported only by the credit of the agency that issued them. Thus, the Fund may
not be able to assert a claim against the United States itself in the event the
agency or instrumentality does not meet its commitment.

SHORT-TERM CORPORATE DEBT INSTRUMENTS. These include commercial paper (including
variable amount master demand notes), which refers to short-term unsecured
promissory notes issued by corporations to finance short-term credit needs.
Commercial paper is usually sold on a discount basis and has a maturity at the
time of issuance not exceeding nine months. In addition, some short-term paper,
which can have a maturity exceeding nine months, is issued in reliance on the
so-called "private placement" exemption from registration afforded by Section
4(2) of the Securities Act of 1933 ("Section 4(2) paper"). The Ready Reserves
Fund portfolio may invest in Section 4(2) paper with maturities of twelve months
or less. Section 4(2) paper is restricted as to disposition under the Federal
securities laws and generally is sold to institutional investors such as the
Fund who agree that they are purchasing the paper for investment and not with a
view to public distribution. Variable amount master demand notes are demand
obligations that permit the investment of fluctuating amounts at varying market
rates of interest pursuant to arrangements between the issuer and a commercial
bank acting as agent for the payees of such notes, whereby both parties have the
right to vary the amount of the outstanding indebtedness on the notes.

Because variable amount master demand notes are direct lending arrangements
between the lender and the borrower, it is not generally contemplated that such
instruments will be traded and there is no secondary market for the notes.
Typically, agreements relating to such notes provide that the lender may not
sell or otherwise transfer the note without the borrower's consent. Such notes
provide that the interest rate on the amount outstanding is adjusted
periodically, typically on a daily basis in accordance with a stated short-term
interest rate benchmark. Since the interest rate of a variable amount master
demand note is adjusted no less often than every 60 days and since repayment of
the note may be demanded at any time, the Fund values such a note in accordance
with the amortized cost basis at the outstanding principal amount of the note.

Also included are nonconvertible corporate debt securities (e.g., bonds and
debentures) with no more than one year remaining to maturity at the date of
settlement. Corporate debt securities with a remaining maturity of less than one
year tend to become quite liquid, have considerably less market value
fluctuations than longer term issues and are traded as money market securities.

BANK MONEY INSTRUMENTS. These include instruments such as certificates of
deposit, time deposits and bankers' acceptances. Certificates of deposit are
generally short-term, interest-bearing negotiable certificates issued by
commercial banks or savings and loan associations against funds deposited in
the issuing institution. A time deposit is a non-negotiable deposit in a
banking institution earning a specified interest rate over a given period of
time. A banker's acceptance is a time draft drawn on a commercial bank by a
borrower usually in connection with an international commercial transaction (to
finance the import, export, transfer or storage of goods). The borrower is
liable for payment as well as the bank, which unconditionally guarantees to pay
the draft at its face amount on the





                                      A-1
<PAGE>   157

maturity date. Most acceptances have maturities of six months or less and are
traded in secondary markets prior to maturity.

REPURCHASE AGREEMENTS. A repurchase agreement is an instrument under which the
purchaser (e.g., a mutual fund) acquires ownership of an obligation (debt
security) and the seller agrees, at the time of the sale, to repurchase the
obligation at a mutually agreed upon time and price, thereby determining the
yield during the purchaser's holding period. This results in a fixed-rate of
return insulated from market fluctuations during such period. The underlying
securities will consist only of U.S. Government or government agency or
instrumentality securities.

Repurchase agreements usually are for short periods, typically less than one
week. Repurchase agreements are considered to be loans under the 1940 Act, with
the security subject to repurchase, in effect, serving as "collateral" for the
loan. The Fund will require the seller to provide additional collateral if the
market value of the securities falls below the repurchase price at any time
during the term of the repurchase agreement. In the event of a default by the
seller because of bankruptcy or otherwise, the Fund may suffer time delays and
incur costs or losses in connection with the disposition of the collateral.




                                      A-2
<PAGE>   158



                                   APPENDIX B

                            COMMERCIAL PAPER RATINGS

A Standard & Poor's commercial paper rating is a current assessment of the
likelihood of timely payment of debt having an original maturity of no more than
365 days. The following summarizes the rating categories used by Standard and
Poor's for commercial paper:

"A-1" - Issue's degree of safety regarding timely payment is strong. Those
issues determined to possess extremely strong safety characteristics are
denoted "A-1+."

"A-2" - Issue's capacity for timely payment is satisfactory. However, the
relative degree of safety is not as high as for issues designated "A-1."

"A-3" - Issue has an adequate capacity for timely payment. It is, however,
somewhat more vulnerable to the adverse effects of changes and circumstances
than an obligation carrying a higher designation.

"B" - Issue has only a speculative capacity for timely payment.

"C" - Issue has a doubtful capacity for payment.

"D" - Issue is in payment default. The "D" category is used when interest
payments or principal payments are not made on the due date, even if the
applicable grace period has not expired when S & P believes such payments will
be made during such grace period.

Moody's commercial paper ratings are opinions of the ability of issuers to repay
punctually promissory obligations not having an original maturity in excess of
one year, unless explicitly noted. The following summarizes the rating
categories used by Moody's for commercial paper:

"Prime-1" - Issuer or related supporting institutions are considered to have a
superior ability for repayment of senior short-term debt obligations. Prime-1
repayment ability will often be evidenced by many of the following
characteristics: leading market positions in well-established industries; high
rates of return on funds employed; conservative capitalization structure with
moderate reliance on debt and ample asset protection; broad margins in earnings
coverage of fixed financial charges and high internal cash generation; and
well-established access to a range of financial markets and assured sources of
alternate liquidity.

"Prime-2" - Issuer or related supporting institutions are considered to have a
strong capacity for repayment of senior short-term debt obligations. This will
normally be evidenced by many of the characteristics cited above but to a lesser
degree. Earnings trends and coverage ratios, while sound, will be more subject
to variation. Capitalization characteristics, while still appropriate, may be
more affected by external conditions. Ample alternative liquidity is maintained.

"Prime-3" - Issuer or related supporting institutions have an acceptable ability
for repayment of senior short-term debt obligations. The effects of industry
characteristics and market composition may be more pronounced. Variability in
earnings and profitability may result in changes in the level of debt protection
measurements and the requirement for relatively high financial leverage.
Adequate alternate liquidity is maintained.

"Not Prime"- Issuer does not fall within any of the Prime rating categories.

The three rating categories of Duff & Phelps for investment grade commercial
paper and short-term debt are "Duff 1," "Duff 2" and "Duff 3." Duff & Phelps
employs three designations, "Duff 1+," "Duff 1" and "Duff 1-," within the
highest rating category. The following summarizes the rating categories used by
Duff & Phelps for commercial paper:





                                      B-1
<PAGE>   159




"Duff 1+" - Debt possesses highest certainty of timely payment. Short-term
liquidity, including internal operating factors and/or access to alternative
sources of funds, is outstanding, and safety is just below risk-free U.S.
Treasury short-term obligations.

"Duff 1" - Debt possesses very high certainty of timely payment. Liquidity
factors are excellent and supported by good fundamental protection factors. Risk
factors are minor.

"Duff 1-" - Debt possesses high certainty of timely payment. Liquidity factors
are strong and supported by good fundamental protection factors. Risk factors
are very small.

"Duff 2" - Debt possesses good certainty of timely payment. Liquidity factors
and company fundamentals are sound. Although ongoing funding needs may enlarge
total financing requirements, access to capital markets is good. Risk factors
are small.

"Duff 3" - Debt possesses satisfactory liquidity, and other protection factors
qualify issue as investment grade. Risk factors are larger and subject to more
variation. Nevertheless, timely payment is expected.

"Duff 4" - Debt possesses speculative investment characteristics. Liquidity is
not sufficient to ensure against disruption in debt service. Operating factors
and market access may be subject to a high degree of variation.

"Duff 5" - Issuer has failed to meet scheduled principal and/or interest
payments.

Fitch short-term ratings apply generally to debt obligations that are payable on
demand or have original maturities of up to three years. The following
summarizes the rating categories used by Fitch for short-term obligations:

"F-1+" - Securities possess exceptionally strong credit quality. Issues assigned
this rating are regarded as having the strongest degree of assurance for timely
payment.

"F-1" - Securities possess very strong credit quality. Issues assigned this
rating reflect an assurance of timely payment only slightly less in degree than
issues rated "F-1+."

"F-2" - Securities possess good credit quality. Issues carrying this rating have
a satisfactory degree of assurance for timely payment, but the margin of safety
is not as great as the "F-1+" and "F-1" categories.

"F-3" - Securities possess fair credit quality. Issues assigned this rating have
characteristics suggesting that the degree of assurance for timely payment is
adequate; however, near-term adverse changes could cause these securities to be
rated below investment grade.

"F-S" - Securities possess weak credit quality. Issues assigned this rating have
characteristics suggesting a minimal degree of assurance for timely payment and
are vulnerable to near-term adverse changes in financial and economic
conditions.

"D" - Securities are in actual or imminent payment default.

                        CORPORATE LONG-TERM DEBT RATINGS

The following summarizes the ratings used by Standard & Poor's for corporate and
municipal debt:

"AAA" - This designation represents the highest rating assigned by Standard &
Poor's. The obligor's capacity to meet its financial commitment is extremely
strong.

"AA" - An obligation rated "AA" differs from the highest rated obligations only
in small degree. The obligor's capacity to meet its financial commitment on the
obligation is very strong.




                                      B-2
<PAGE>   160




"A" - An obligation rated "A" is somewhat more susceptible to the adverse
effects of changes in circumstances and economic conditions than obligations in
higher-rated categories. However, the obligor's capacity to meet its financial
commitment on the obligation is still strong.

"BBB" - An obligation rated "BBB" exhibits adequate protection parameters.
However, adverse economic conditions or changing circumstances are more likely
to lead to a weakened capacity of the obligor to meet its financial commitment
on the obligation.

"BB," "B," "CCC," "CC," and "C" - Debt is regarded as having significant
speculative characteristics. "BB" indicates the least degree of speculation and
"C" the highest. While such obligations will likely have some quality and
protective characteristics, these are outweighed by large uncertainties or major
risk exposures to adverse conditions.

"BB" - Debt is less vulnerable to non-payment than other speculative issues.
However, it faces major ongoing uncertainties or exposure to adverse business,
financial or economic conditions which could lead to obligor's inadequate
capacity to meet its financial commitment on the obligation.

"B" - Debt is more vulnerable to non-payment than obligations rated "BB," but
the obligor currently has the capacity to meet its financial commitment on the
obligation. Adverse business, financial or economic conditions will likely
impair the obligor's capacity or willingness to meet its financial commitment on
the obligation.

"CCC" - Debt is currently vulnerable to non-payment, and is dependent upon
favorable business, financial and economic conditions for the obligor to meet
its financial commitment on the obligation. In the event of adverse business,
financial or economic conditions, the obligor is not likely to have the capacity
to meet its financial commitment on the obligation.

"CC" - An obligation rated "CC" is currently highly vulnerable to non-payment.

"C" - The "C" rating may be used to cover a situation where a bankruptcy
petition has been filed or similar action has been taken, but payments on this
obligation are being continued.

"D" - An obligation rated "D" is in payment default. This rating is used when
payments on an obligation are not made on the date due, even if the applicable
grace period has not expired, unless S & P believes that such payments will be
made during such grace period. "D" rating is also used upon the filing of a
bankruptcy petition or the taking of similar action if payments on an obligation
are jeopardized.

PLUS (+) OR MINUS (-) - The ratings from "AA" through "CCC" may be modified by
the addition of a plus or minus sign to show relative standing within the major
rating categories.

"r" - This rating is attached to highlight derivative, hybrid, and certain other
obligations that S & P believes may experience high volatility or high
variability in expected returns due to non-credit risks. Examples of such
obligations are: securities whose principal or interest return is indexed to
equities, commodities or currencies; certain swaps and options; and
interest-only and principal-only mortgage securities. The absence of an "r"
symbol should not be taken as an indication that an obligation will exhibit no
volatility or variability in total return.

The following summarizes the ratings used by Moody's for corporate and municipal
long-term debt:

"Aaa" - Bonds are judged to be of the best quality. They carry the smallest
degree of investment risk and are generally referred to as "gilt edge." Interest
payments are protected by a large or by an exceptionally stable margin and
principal is secure. While the various protective elements are likely to change,
such changes as can be visualized are most unlikely to impair the fundamentally
strong position of such issues.

"Aa" - Bonds are judged to be of high quality by all standards. Together with
the "Aaa" group they comprise what are generally known as high-grade bonds.
They are rated lower than the best bonds because margins of protection may not
be as large as in "Aaa" securities or fluctuation of protective elements may be
of greater amplitude or there may be other elements present which make the
long-term risks appear somewhat larger than in "Aaa" securities.





                                      B-3
<PAGE>   161

"A" - Bonds possess many favorable investment attributes and are to be
considered as upper-medium-grade obligations. Factors giving security to
principal and interest are considered adequate but elements may be present which
suggest a susceptibility to impairment sometime in the future.

"Baa" - Bonds considered medium-grade obligations, i.e., they are neither highly
protected nor poorly secured. Interest payments and principal security appear
adequate for the present but certain protective elements may be lacking or may
be characteristically unreliable over any great length of time. Such bonds lack
outstanding investment characteristics and in fact have speculative
characteristics as well.

"Ba," "B," "Caa," "Ca," and "C" - Bonds that possess one of these ratings
provide questionable protection of interest and principal ("Ba" indicates some
speculative elements; "B" indicates a general lack of characteristics of
desirable investment; "Caa" represents a poor standing; "Ca" represents
obligations which are speculative in a high degree; and "C" represents the
lowest rated class of bonds). "Caa," "Ca" and "C" bonds may be in default.

Con. (--) - Bonds for which the security depends upon the completion of some act
or the fulfillment of some condition are rated conditionally. These are bonds
secured by (a) earnings of projects under construction, (b) earnings of projects
unseasoned in operation experience, (c) rentals which begin when facilities are
completed, or (d) payments to which some other limiting condition attaches.
Parenthetical rating denotes probable credit stature upon completion of
construction or elimination of basis of condition.

(P) - When applied to forward delivery bonds, indicates that the rating is
provisional pending delivery of the bonds. The rating may be revised prior to
delivery if changes occur in the legal documents or the underlying credit
quality of the bonds.

Note: Those bonds in the Aa, A, Baa, Ba and B groups which Moody's believes
possess the strongest investment attributes are designated by the symbols Aa1,
A1, Baa1, Ba1 and B1.

The following summarizes the ratings used by Duff & Phelps for corporate and
municipal long-term debt:

"AAA" - Debt is considered to be of the highest credit quality. The risk factors
are negligible, being only slightly more than for risk-free U.S. Treasury debt.

"AA" - Debt is considered of high credit quality. Protection factors are strong.
Risk is modest but may vary slightly from time to time because of economic
conditions.

"A" - Debt possesses protection factors which are average but adequate. However,
risk factors are more variable and greater in periods of economic stress.

"BBB" - Debt possesses below average protection factors but such protection
factors are still considered sufficient for prudent investment. Considerable
variability in risk is present during economic cycles.

"BB," "B," "CCC," "DD," and "DP" - Debt that possesses one of these ratings is
considered to be below investment grade. Although below investment grade, debt
rated "BB" is deemed likely to meet obligations when due. Debt rated "B"
possesses the risk that obligations will not be met when due. Debt rated "CCC"
is well below investment grade and has considerable uncertainty as to timely
payment of principal, interest or preferred dividends. Debt rated "DD" is a
defaulted debt obligation, and the rating "DP" represents preferred stock with
dividend averages.

To provide more detailed indications of credit quality, the "AA," "A," "BBB,"
"BB" and "B" ratings may be modified by the addition of a plus (+) or minus (-)
sign to show relative standing within these major categories.

The following summarizes the highest four ratings used by Fitch for corporate
and municipal bonds:

"AAA" - Bonds considered to be investment grade and of the highest credit
quality. The obligor has an exceptionally strong ability to pay interest and
repay principal, which is unlikely to be affected by reasonably foreseeable
events.




                                      B-4
<PAGE>   162

"AA" - Bonds considered to be investment grade and of very high credit quality.
The obligor's ability to pay interest and repay principal is very strong,
although not quite as strong as bonds rated "AAA." Because bonds rated in the
"AAA" and "AA" categories are not significantly vulnerable to foreseeable future
developments, short-term debt of these issuers is generally rated "F-1+."

"A" - Bonds considered to be investment grade and of high credit quality. The
obligor's ability to pay interest and repay principal is considered to be
strong, but may be more vulnerable to adverse changes in economic conditions and
circumstances than bonds with higher ratings.

"BBB" - Bonds considered to be investment grade and of satisfactory credit
quality. The obligor's ability to pay interest and repay principal is considered
to be adequate. Adverse changes in economic conditions and circumstances,
however, are more likely to have an adverse impact on these bonds and,
therefore, impair timely payment. The likelihood that the ratings of these bonds
will fall below investment grade is higher than for bonds with higher ratings.

"BB" - Bonds considered to be speculative. The obligor's ability to pay interest
and repay principal may be affected over time by adverse economic changes.
However, business and financial alternatives can be identified, which could
assist the obligor in satisfying its debt service requirements.

"B" - Bonds are considered highly speculative. While securities in this class
are currently meeting debt service requirements, the probability of continued
timely payment of principal and interest reflects the obligor's limited margin
of safety and the need for reasonable business and economic activity throughout
the life of the issue.

"CCC " - Bonds have certain identifiable characteristics that, if not remedied,
may lead to default. The ability to meet obligations requires an advantageous
business and economic environment.

"CC" - Bonds are minimally protected. Default in payments of interest and/or
principal seems probable over time.

"C" - Bonds are in imminent default in payment of interest or principal.

"DDD," "DD" and "D" - Bonds are in default on interest and/or principal
payments. Such securities are extremely speculative and should be valued on the
basis of their ultimate recovery value in liquidation or reorganization of the
obligor. "DDD" represents the highest potential for recovery on these
securities, and "D" represents the lowest potential for recovery.

To provide more detailed indications of credit quality, the Fitch ratings from
and including "AA" to "C" may be modified by the addition of a plus (+) or minus
(-) sign to show relative standing within these major rating categories.


                                      B-5
<PAGE>   163

                        WILLIAM BLAIR MUTUAL FUNDS, INC.

                                     PART C

                               OTHER INFORMATION

ITEM 23.          EXHIBITS

                  (a)      (i)      Articles of Incorporation. (1)/
                           (ii)     Form of Amendment to Articles of
                                    Incorporation. (1)/

                  (b)      By-laws, as amended. (4)/

                  (c)      None.

                  (d)      (i)      Form of Management Agreement dated May 1,
                                    1996, as amended. (3)/
                           (ii)     Form of Management Agreement dated December
                                    23, 1996. (2)/
                           (iii)    Form of Management Agreement dated April 30,
                                    1998. (4)/

                  (e)      (i)      Underwriting Agreement. (1)/
                           (ii)     Form of Distribution Agreement -- Class B
                                    and Class C.*

                  (f)      None.

                  (g)      (i)    Custodian Agreement. (1)/
                           (ii)   Delegation Agreement. (4)/

                  (h)      Form of Shareholder Services Agreement -- Class A,
                           Class B and Class C*.

                  (i)      Opinion and Consent of Vedder, Price, Kaufman &
                           Kammholz. **


                  (j)      Consent of Ernst & Young LLP.*


                  (k)      Not applicable.

                  (l)      Subscription Agreement. (1)/

                  (m)      Form of Distribution Plan -- Class B and Class C.*

                  (n)      Not applicable.

                  (o)      Form of Multi-Class Plan.*

                  (p)      Powers of Attorney. (4)/

- ------------------

(1)/     Incorporated herein by reference to Post-Effective Amendment No. 13 to
         Registrant's Registration Statement on Form N-1A as filed on or about
         March 1, 1996.

(2)/     Incorporated herein by reference to Post-Effective Amendment No. 15 to
         Registrant's Registration Statement on Form N-1A as filed on or about
         November 5, 1996.

(3)/     Incorporated herein by reference to Post-Effective Amendment No. 16 to
         Registrant's Registration Statement on Form N-1A as filed on or about
         February 26, 1997.

(4)/     Incorporated herein by reference to Post-Effective Amendment No. 17 to
         Registrant's Registration Statement on Form N-1A as filed on or about
         February 27, 1998.

*        Filed herewith.

**       To be filed by amendment.



                                      C-1
<PAGE>   164



ITEM 24.          Persons Controlled by or Under Common Control with Registrant

                  Not applicable.

ITEM 25.          Indemnification

         Section 2-418 of the Maryland General Corporation Law provides for
indemnification of directors, officers, employees and agents.

         Article XII of the Registrant's Articles of Incorporation provides for
indemnification of directors and officers under certain circumstances but does
not allow such indemnification in cases of willful misfeasance, bad faith, gross
negligence, or reckless disregard of the duties involved in the conduct of his
office.

         The Investment Management Agreement between the Registrant and William
Blair & Company, L.L.C. (the "Adviser") provides that, in the absence of willful
misfeasance, bad faith, gross negligence or reckless disregard of obligations or
duties thereunder on the part of the Adviser, the Adviser shall not be liable
for any error of judgment or mistake of law, or for any loss suffered by the
Fund in connection with the matters to which such Agreement relates.

         Insofar as indemnification for liabilities arising under the Securities
Act of 1933 (the "1933 Act") may be permitted to directors, officers, and
controlling persons of the Registrant pursuant to the foregoing provisions, or
otherwise, the Registrant has been advised that in the opinion of the Securities
and Exchange Commission such indemnification is against public policy as
expressed in the 1933 Act and is, therefore, unenforceable. In the event that a
claim for indemnification against such liabilities (other than the payment by
the Registrant of expenses incurred or paid by a director, officer, or
controlling person of the Registrant in the successful defense of any action,
suit, or proceeding) is asserted by such director, officer, or controlling
person in connection with the securities being registered, the Registrant will,
unless in the opinion of its counsel the matter has been settled by controlling
precedent, submit to a court of appropriate jurisdiction the question whether
such indemnification by it is against public policy as expressed in the 1933 Act
and will be governed by the final adjudication of such issue.

ITEM 26.          Business and Other Connections of Investment Adviser

         Registrant's investment manager is William Blair & Company, L.L.C., a
limited liability company. In addition to its services to Registrant as
investment manager as set forth in Parts A and B of this Registration Statement
on Form N-1A, William Blair & Company, L.L.C. is a registered broker-dealer and
investment adviser and engages in investment banking.

         The principal occupations of the principals and primary officers of
William Blair & Company, L.L.C. are their services as principals and officers
of that Company. The address of William Blair & Company, L.L.C. and Registrant
is 222 West Adams Street, Chicago, Illinois 60606.

         Set forth below is information as to any other business, profession,
vocation or employment of a substantial nature in which each principal of
William Blair & Company, L.L.C. is, or at any time during the last two fiscal
years has been, engaged for his own account or in the capacity of director,
officer, employee, partner or trustee:


<TABLE>
<CAPTION>
         NAME AND POSITION WITH
    WILLIAM BLAIR & COMPANY, L.L.C.      PRINCIPAL BUSINESS                       CAPACITY
    -------------------------------      ------------------                       --------

<S>                                      <C>                                      <C>
Michael Balkin                           The New Providence Fund                  General Partner
Principal
</TABLE>



                                      C-2
<PAGE>   165



<TABLE>
<CAPTION>
         NAME AND POSITION WITH
    WILLIAM BLAIR & COMPANY, L.L.C.      PRINCIPAL BUSINESS                       CAPACITY
    -------------------------------      ------------------                       --------

<S>                                      <C>                                      <C>
Rocky Barber                             LaRabida Hospital Foundation             Vice President of the Board of Directors
Principal                                Metropolitan Chicago YMCA                Director
                                         Metropolitan Club                        Board Member
                                         Stanford Business School                 Member Advisory Council
                                         William Blair Mutual Funds, Inc.         Chief Executive Officer

Bowen Blair,                             The Art Institute of Chicago             Trustee
Senior Principal                         Chicago Historical Society               Trustee
                                         Field Museum of Natural History          Trustee

Edward McC. Blair, Sr.,                  The Art Institute of Chicago             Life Trustee
Senior Principal                         College of The Atlantic                  Board of Trustees
                                         Pullman Educational Foundation           Life Trustee
                                         Rush Presbyterian-St. Luke's             Life Trustee
                                         Medical Center
                                         University of Chicago                    Life Trustee
Edward McC. Blair, Jr.,                  Chicago Dock and Canal Trust             Trustee
Principal                                Chicago Zoological Society               Deputy Chairman
                                         Research Medical, Inc.                   Director
                                         University of Chicago Hospital           Trustee

Kurt Beuchel,                            Social Security Fund of the Principality Member, Investment Advisory Board
Principal                                Liechtenstein

George Busse                             Busse Venture Associates                 Partner
Principal                                George L. Busse & Co.                    Director
                                         Mount Prospect National Bank             Director

David G. Chandler,                       Electronic Manufacturing Systems, Inc.   Director
Principal                                Encore Paper Company                     Director
                                         Engineered Materials Corp.               Director
                                         Gibraltar Packaging Group                Director
                                         Harmonic Systems, Inc.                   Director
                                         Morton Grove Pharmaceuticals, Inc.       Director
                                         Pacwest Telecom, Inc.                    Director
                                         Pharma Research Corp.                    Director
                                         Predelivery Service Corporation          Director
                                         Sweetwater Sound, Inc.                   Director

E. David Coolidge, III,                  Pittway Corporation                      Director
Chief Executive Officer

Conrad Fischer,                          APM Limited Partnership                  General Partner
Principal                                Chicago Child Care                       Trustee, Emeritus
                                         Kalamazoo College                        Investment Committee
                                         William Blair Mutual Funds, Inc.         Chairman and Director
</TABLE>



                                      C-3
<PAGE>   166



<TABLE>
<CAPTION>
         NAME AND POSITION WITH
    WILLIAM BLAIR & COMPANY, L.L.C.      PRINCIPAL BUSINESS                       CAPACITY
    -------------------------------      ------------------                       --------

<S>                                      <C>                                      <C>
Mark A. Fuller, III,                     Fuller Investment Company                President
Principal                                Fulsen Howney Partners                   Partner
                                         Three Rio Grande, LLC                    Principal
                                         William Blair Mutual Funds, Inc.         Senior Vice President

John K. Greene,                          Chicago Horticultural Society            Trustee
Principal                                Children's Home & Aid Society            Trustee
                                         of Illinois, Inc.
                                         Garden Conservatory                      Trustee
                                         Hazelden                                 Chairman, Illinois Board of Directors
                                         Vulcan Materials Co.                     Director

James P. Hickey,                         Eagle Point Software                     Director
Principal

Edgar D. Jannotta, Sr.,                  AAR Corporation                          Director
Senior Principal                         AON Corporation                          Director
                                         Bandag, Incorporated                     Director
                                         Molex, Incorporated                      Director
                                         Oil-Dri Corporation of America           Director
                                         Sloan Valve Company                      Director
                                         Unicom Corporation                       Director

Richard P. Kiphart,                      McCormick Theological Seminary           Board of Directors
Principal                                Concord EFS, Inc.                        Director

Charles Kraft,                           Spartan Holdings LLC                     President
Principal                                Dalton, Grenar, Hartman, Maher LP        Limited Partner

Robert Lamphier, IV,                     Ag. Med, Inc.                            Chairman
Principal

James McMullan,                          University of Mississippi Foundation     Director
Principal                                William Blair Mutual Funds, Inc.         Director

David W. Morrison,                       Bell Flavors & Fragrances, Inc.          Director
Principal

Timothy M. Murray,                       Daisytek International                   Director
Principal                                Mede America, Inc.                       Director
                                         Portland Food Products, Incorporated     Director
                                         Towne Holdings, Inc.                     Director
</TABLE>




                                      C-4
<PAGE>   167


<TABLE>
<CAPTION>
         NAME AND POSITION WITH
    WILLIAM BLAIR & COMPANY, L.L.C.      PRINCIPAL BUSINESS                       CAPACITY
    -------------------------------      ------------------                       --------

<S>                                      <C>                                      <C>
Bentley M. Myer,                         Delnor Community Hospital                Director
Principal                                William Blair Mutual Funds, Inc.         Senior Vice President

David G. O'Neill,                        Elder Care Information Network           Director
Principal                                Resume Link, Inc.                        Director
                                         Svboda, Collins & Co.                    Advisory Board

Phillip Reitz,                           Fairway Drive Funding Corp.              Director
Principal                                Worcester Co.                            Director
                                         XOLOX Corporation                        Advisory Board

Neal L. Seltzer,                         Scholarship and Guidance Foundation      Director
Principal                                Lake Shore Country Club                  Director
                                         Serendipity Fund II, L.P.                General Partner
                                         New Providence Fund, L.P.                General Partner

William Semmer,                          Chicago Home and Garden Magazine         Director
Principal

Thomas H. Story,                         Security APL, Inc.                       Member, Advisory Council
Principal

Mark Timmerman,                          DIY Home Warehouse, Incorporated         Director
Principal                                Prophet 21, Incorporated                 Director

W. James Truettner, Jr.,                 Glenview Foundation                      Director
Principal                                International Travel Services            Director

Kathleen A. Wieland,                     Blue Egg Enterprises                     President
Principal                                D/B/A Robin's Bookshop
</TABLE>


ITEM 27.          Principal Underwriters

                  (a)      Not applicable.

                  (b)      The principal business address of each principal and
                           officer of William Blair & Company, L.L.C., principal
                           underwriter for Registrant, is 222 West Adams Street,
                           Chicago, Illinois 60606. See Item 26 for information
                           with respect to officers and principals of William
                           Blair & Company, L.L.C.

                  (c)      Not applicable.






                                      C-5
<PAGE>   168

ITEM 28.          Location of Accounts and Records

         All such accounts, books and other documents are maintained by the
Registrant's officers at the offices of the Registrant and the offices of the
Investment Adviser, William Blair & Company, L.L.C., 222 West Adams Street,
Chicago, Illinois 60606. Shareholder account information and original
shareholder correspondence is also available at the offices of the Transfer
Agent and Dividend Paying Agent, State Street Bank and Trust Company, P.O. Box
9104, Boston, Massachusetts 02266-9104.

ITEM 29.          Management Services

                  Not applicable.

ITEM 30.          Undertakings

                  Not applicable.


                                      C-6
<PAGE>   169




                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933 and the
Investment Company Act of 1940, the registrant has duly caused this amended
registration statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Chicago, and State of Illinois, on the 28th day
of July, 1999.

                              WILLIAM BLAIR MUTUAL FUNDS, INC.


                              By:  /s/  MARCO HANIG
                                 ----------------------------------------
                                        Marco Hanig, President

         Pursuant to the requirements of the Securities Act of 1933, this
post-effective amendment to the registration statement has been signed below by
the following persons in the capacity indicated and on the 28th day of July,
1999.


SIGNATURE                               TITLE
- ---------                               -----

/s/ VERNON ARMOUR*                      Director
- -----------------------------
Vernon Armour

/s/ J. GRANT BEADLE*                    Director
- -----------------------------
J. Grant Beadle

/s/ THEODORE A. BOSLER*                 Director
- -----------------------------
Theodore A. Bosler

/s/ CONRAD FISCHER                      Director (Chairman of the Board)
- -----------------------------
Conrad Fischer

/s/ ANN P. MCDERMOTT*                   Director
- -----------------------------
Ann P. McDermott

/s/ JAMES M. MCMULLAN*                  Director
- -----------------------------
James M. McMullan

/s/ JOHN B. SCHWEMM*                    Director
- -----------------------------
John B. Schwemm

/s/ MARCO HANIG                         President (Principal Executive Officer)
- -----------------------------
Marco Hanig

/s/ TERENCE M. SULLIVAN                 Treasurer (Principal Financial Officer,
- -----------------------------           Principal Accounting Officer)
Terence M. Sullivan

- ------------------

*   Conrad Fischer signs this document pursuant to a power of attorney
    incorporated herein by reference to Post-Effective Amendment No. 17 to
    Registrant's Registration Statement on Form N-1A as filed on or about
    February 27, 1998.


<PAGE>   170



                                 EXHIBIT INDEX

<TABLE>
<CAPTION>
EXHIBIT
NUMBER    DESCRIPTION
- ------    -----------

<S>       <C>
(e)(ii)   Form of Distribution Agreement -- Class B and Class C.

(h)       Form of Shareholder Services Agreement -- Class A, Class B and
          Class C.

(j)       Consent of Ernst & Young LLP.

(m)       Form of Distribution Plan -- Class B and Class C.

(o)       Form of Multi-Class Plan.
</TABLE>

<PAGE>   1

                                                                 Exhibit (e)(ii)



                             DISTRIBUTION AGREEMENT

                                 (CLASS B AND C)


     AGREEMENT made as of this ___ day of ________, 1999 by and between
WILLIAM BLAIR MUTUAL FUNDS, INC., a Maryland corporation (the "Company") and
WILLIAM BLAIR & COMPANY, L.L.C., an Illinois limited liability company ("William
Blair").

     WHEREAS, the Company is registered under the Investment Company Act of
1940, as amended (the "1940 Act"), as an open-end management investment company
which offers for public sale separate series of shares of beneficial interest,
each corresponding to a distinct portfolio which may be further divided into
separate classes of shares (the "Shares"); and

     WHEREAS, the Company has adopted a Distribution Plan pursuant to Rule
12b-1 under the 1940 Act (the "Plan") on behalf of each of its series (except
the Ready Reserves Fund) (the "Funds") for its Class B and C shares; and

     WHEREAS, the Company desires to enter into this Distribution Agreement
(the "Agreement") with William Blair pursuant to which William Blair agrees to
provide distribution-related service to the Class B and C shares of each Fund;

     NOW, THEREFORE, the parties agree as follows:

     1.  A. The Company, on behalf of each Fund, is authorized to pay to William
Blair, as compensation for distribution-related services that are primarily
intended to result in the sale of the Funds, the distribution fees which are
specified in the Plan. Fees are to be paid by the Funds as described in the
Plan, or at such other intervals as the Company's Board of Directors (the
"Board") shall determine, computed at the annual rate of .75% of the average
daily net assets attributable to the Class B and C shares of each Fund.

         B. Any Fund may pay distribution fees for its Class B and C shares to
William Blair at a lesser rate than the fees specified in the Plan as agreed
upon by the Board and William Blair.

     2.  As distributor of the Funds, William Blair may spend such amounts as it
deems appropriate on any activities or expenses primarily intended to result in
the sale of the Funds, including but not limited to: compensation to employees
or independent contractors of William Blair; compensation to and expenses of
William Blair and other selected dealers who engage in or




<PAGE>   2

support the distribution of the Funds, including overhead and telephone and
other communication expenses; the printing of prospectuses, statements of
additional information and reports for other than existing shareholders, the
preparation, printing and distribution of sales literature and advertising
materials, and other direct and indirect distribution-related expenses.

     3.  This Agreement shall not take effect with respect to any Fund unless it
has been approved, together with any related agreements, by a majority vote,
cast in person at a meeting (or meetings) called for the purpose of voting on
such approval, of (a) the Board; and (b) those Directors of the Company who are
not "interested persons" of the Company, as defined under the Act, and have no
direct or indirect financial interest in the operation of this Agreement or any
agreements related thereto (the "Independent Board Members").

     4.  William Blair shall provide to the Board and the Board shall review, at
least quarterly, a written report of the amounts expended with respect to each
Fund under this Agreement and the purposes for which such expenditures were
made.

     5.  The Company or any Fund may terminate this Agreement at any time,
without the payment of any penalty, by vote of the Board, by vote of a majority
of the Independent Board Members, or by vote of a majority of the outstanding
voting securities of the affected Fund.

     6.  This Agreement may not be amended to increase materially the amount of
distribution fees to be paid by a Fund unless amendment of the Plan is approved
by a vote of a majority of the outstanding voting securities of the affected
Fund, and no material amendment to the other provisions of the Agreement shall
be made unless approved in the manner provided for approval in Section 6 of the
Plan.

     7.  The amount of the distribution fees payable by any Fund for the B and C
Class under this Agreement and any distribution agreement may be greater or
lesser than the distribution-related expenses actually incurred on behalf of
such Fund. The distribution fees set forth in the Plan with respect to a Fund
will be payable by such Fund until the Agreement is terminated or not renewed
with respect to the shares of that Fund.

     8.  As used in this Agreement, the terms "majority of the outstanding
voting securities," "assignment" and "interested person" shall have the same
meaning as those terms have in the 1940 Act.

     9.  The Company shall preserve copies of this Agreement (including any
amendments thereto) and any related agreements and all reports made pursuant to
paragraph 4 hereof for a period of not less than six years from the date
thereof, the first two years in an easily accessible place.



                                       2
<PAGE>   3




         IN WITNESS WHEREOF, the Company and William Blair have caused this
Agreement to be executed as of the day and year first above written.

                                           WILLIAM BLAIR MUTUAL FUNDS, INC.



Attest:                                    By:
       ----------------------------           -------------------------------


                                           WILLIAM BLAIR & COMPANY, L.L.C.



Attest:                                    By:
       ----------------------------           -------------------------------





                                       3

<PAGE>   1

                                                                     Exhibit (h)



                         SHAREHOLDER SERVICES AGREEMENT

                               (CLASS A, B AND C)

         AGREEMENT made as of this ___ day of __________, 1999 by and between
WILLIAM BLAIR MUTUAL FUNDS, INC., a Maryland corporation (the "Company") and
WILLIAM BLAIR & COMPANY, L.L.C., an Illinois limited liability company ("William
Blair").

         In consideration of the mutual covenants hereinafter contained, it is
hereby agreed by and between the parties hereto as follows:

     1.  The Company hereby appoints William Blair to provide information and
shareholder services for the benefit of the Company and its shareholders. In
this regard, William Blair shall appoint various broker-dealer firms and other
service firms ("Firms") to provide related services and facilities for persons
who are investors in the Company ("investors"). The Firms shall provide such
office space and equipment, telephone facilities, personnel or other services as
may be necessary or beneficial for providing information and services to
investors in the Company. Such services and assistance may include, but are not
limited to, establishing and maintaining accounts and records, processing
purchase and redemption transactions, answering routine inquiries regarding the
Company and the Funds and special features available to shareholders, assistance
to investors in changing dividend and investment options, account designations
and addresses, and such other services as the Company or William Blair may
reasonably request. Firms may include affiliates of William Blair. William Blair
may also provide some of the above services for the Company directly.

         William Blair accepts such appointment and agrees during such period to
render such services and to assume the obligations herein set forth for the
compensation herein provided. William Blair shall for all purposes herein
provided be deemed to be an independent contractor and, unless otherwise
expressly provided or authorized, shall have no authority to act for or
represent the Company in any way or otherwise be deemed an agent of the Company.
William Blair, by separate agreement with the Company, may also serve the
Company in other capacities. In carrying out its duties and responsibilities
hereunder, William Blair will appoint various Firms to provide services
described herein directly to or for the benefit of investors in the Company.
Such firms shall at all times be deemed to be independent contractors retained
by William Blair and not the Company. William Blair and not the Company will be
responsible for the payment of compensation to such Firms for such services.


     2.  For the shareholder services and facilities described in Section 1, the
Company will pay to William Blair at the end of each calendar month a
shareholder services fee computed at an annual rate of up to 0.25 of 1% of the
average daily net assets of each Class A, B and C share of each separate series
(each a "Fund") of the Company. The shareholder services fee will be calculated




<PAGE>   2

separately for each Class A, B and C share of a Fund as an expense of each such
class. For the month and year in which this Agreement becomes effective or
terminates, there shall be an appropriate proration on the basis of the number
of days that the Agreement is in effect during such month and year,
respectively. The services of William Blair to the Company under this Agreement
are not to be deemed exclusive, and William Blair shall be free to render
similar services or other services to others.

         The net asset value for each share of a Fund shall be calculated in
accordance with the provisions of the Company's current prospectus. On each day
when net asset value is not calculated, the net asset value of a share of each
Fund shall be deemed to be the net asset value of such a share as of the close
of business on the last day on which such calculation was made for the purpose
of the foregoing computations.

     3.  The Company shall assume and pay all charges and expenses of its
operations not specifically assumed or otherwise to be provided by William Blair
under this Agreement.

     4.  This Agreement may be terminated at any time without the payment of any
penalty by the Company or by William Blair on sixty (60) days written notice to
the other party. Termination of this Agreement shall not affect the right of
William Blair to receive payments on any unpaid balance of the compensation
described in Section 2 hereof earned prior to such termination. All material
amendments to this Agreement must be approved by vote of the Board of Directors
of the Company.

     5. If any provision of this Agreement shall be held or made invalid by a
court decision, statute, rule or otherwise, the remainder shall not be thereby
affected.

     6.  Any notice under this Agreement shall be in writing, addressed and
delivered or mail, postage prepaid, to the other party at such address as such
other party may designate for the receipt of such notice.

     7.  This Agreement shall be construed in accordance with applicable federal
law and the laws of the State of Illinois.

                      [SIGNATURES APPEAR ON THE NEXT PAGE]





                                       2

<PAGE>   3


         IN WITNESS WHEREOF, the Company and William Blair have caused this
Agreement to be executed as of the day and year first above written.

                                             WILLIAM BLAIR MUTUAL FUNDS, INC.



Attest:                                      By:
       -------------------------------           -------------------------------


                                             WILLIAM BLAIR & COMPANY, L.L.C.



Attest:                                      By:
       -------------------------------           -------------------------------








                                       3

<PAGE>   1
                                                                     EXHIBIT (J)

                        CONSENT OF INDEPENDENT AUDITORS

     We consent to the references to our firm under the captions "Financial
Highlights" and "Independent Auditors" and to the use of our report dated
February 2, 1999 for William Blair Mutual Funds, Inc. (comprised of the Growth
Fund, Value Discovery Fund, International Growth Fund, Emerging Markets Growth
Fund, Income Fund and Ready Reserves Fund) in the Registration Statement (Form
N-1A) and its incorporation by reference in the related Prospectus and Statement
of Additional Information, filed with the Securities and Exchange Commission in
this Post-Effective Amendment No. 20 to the Registration Statement under the
Securities Act of 1933 (Registration No. 33-17463) and in this Amendment No. 21
to the Registration Statement under the Investment Company Act of 1940
(Registration No. 811-5344).


                                             /s/ ERNST & YOUNG LLP
                                             -------------------------------
                                             ERNST & YOUNG LLP

Chicago, Illinois

<PAGE>   1


                                                                   Exhibit (m)

                                DISTRIBUTION PLAN

                                 (CLASS B AND C)

     Pursuant to the provisions of Rule 12b-1 under the Investment Company Act
of 1940 (the "Act"), this Distribution Plan (the "Plan") has been adopted for
Class B and C shares of each series (except the Ready Reserves Fund) (each a
"Fund") of the William Blair Mutual Funds, Inc. (the "Company") by a majority of
the members of the Company's Board of Directors (the "Board"), including a
majority of the Board members who are not "interested persons" of the Company as
defined in the Act and who have no direct or indirect financial interest in the
operation of the Plan or in any agreements related to the Plan (the "Independent
Board Members") at a meeting called for the purpose of voting on this Plan.

     1. Compensation. The Company will pay to William Blair & Company, L.L.C.
("William Blair") at the end of each calendar month a distribution services fee
computed at the annual rate of .75% of average daily net assets attributable to
the Class B and C shares of each Fund. William Blair may compensate various
financial service firms appointed by William Blair ("Firms") in accordance with
the provisions of the Company's Distribution Agreement for Class B and C shares
(the "Distribution Agreement") for sales of shares at the fee levels provided in
the Company's prospectus from time to time. William Blair may pay other
commissions, fees or concessions to Firms, and may pay them to others in its
discretion, in such amounts as William Blair shall determine from time to time.
The distribution services fee for each Class of a Fund shall be based upon
average daily net assets of a Fund attributable to each B and C Class and such
fee shall be charged only to that Class. For the month and year in which this
Plan becomes effective or terminates, there shall be an appropriate proration of
the distribution services fee set forth in Paragraph 1 hereof on the basis of
the number of days that the Plan and any agreement related to the Plan are in
effect during the month and year, respectively. The distribution services fee
shall be in addition to and shall not be reduced or offset by the amount of any
contingent deferred sales charge received by William Blair for a Class.

     2. Shareholder Approval. Implementation of the Plan is subject to
shareholder approval.

     3. Periodic Reporting. William Blair shall prepare reports for the Board on
a quarterly basis for the B and C Class of each Fund showing amounts paid to the
various Firms and such other information as from time to time shall be
reasonably requested by the Board.

     4. Continuance. This Plan shall continue in effect indefinitely, provided
that such continuance is approved at least annually by a vote of a majority of
the Board, and of the Independent Board Members, cast in person at a meeting
called for such purpose or by vote of at least a majority of the outstanding
voting securities of the B and C Class of each Fund.



<PAGE>   2


     5.  Termination. This Plan may be terminated at any time without penalty
with respect to either the B or C Class by vote of a majority of the Independent
Board Members or by vote of the majority of the outstanding voting securities of
either Class of any Fund.

     6.  Amendment. This Plan may not be amended to increase materially the
amount to be paid to William Blair by each Fund for distribution services with
respect to the B and C Class without the vote of a majority of the outstanding
voting securities of that Class. All material amendments to this Plan must in
any event be approved by a vote of a majority of the Board, and of the
Independent Board Members, cast in person at a meeting called for such purpose
or in any other manner permitted by the Act.

     7.  Selection of Non-Interested Board Members. So long as this Plan is in
effect, the selection and nomination of those Board members who are not
interested persons of the Company will be committed to the discretion of Board
members who are not themselves interested persons.

     8.  Recordkeeping. The Company will preserve copies of this Plan, the
Distribution Agreement, and all reports made pursuant to Paragraph 2 above for a
period of not less than six (6) years from the date of this Plan, the
Distribution Agreement, or any such report, as the case may be, the first two
(2) years in an easily accessible place.

     9.  Limitation of Liability. Any obligation of the Company hereunder shall
be binding only upon the assets of the B and C Class of each Fund and shall not
be binding on any Board member, officer, employee, agent, or shareholder of the
Company. Neither the authorization of any action by the Board members or
shareholders of the Company nor the adoption of the Plan on behalf of the
Company shall impose any liability upon any Board member or upon any
shareholder.

     10. Definitions. The terms "interested person" and "vote of a majority of
the outstanding voting securities" shall have the meanings set forth in the Act
and the rules and regulations thereunder.

     11. Severability; Separate Action. If any provision of this Plan shall be
held or made invalid by a court decision, rule or otherwise, the remainder of
this Plan shall not be affected thereby. Action shall be taken separately for
the B and C Class as the Act or the rules thereunder so require.

Dated: July 20, 1999.





                                       2

<PAGE>   1


                                                                Exhibit (o)



                        WILLIAM BLAIR MUTUAL FUNDS, INC.

                                MULTI-CLASS PLAN


         WHEREAS, the William Blair Mutual Funds, Inc. (the "Company") is an
open-end management investment company registered under the Investment Company
Act of 1940 (the "1940 Act") with authorized separate series ("Funds");

         WHEREAS, William Blair & Company, L.L.C. ("William Blair") serves as
investment manager and principal underwriter for the Company;

         WHEREAS, as described in its prospectus, each Fund (except the Ready
Reserves Fund) has established multiple classes enabling each Fund to offer
investors the option of purchasing shares (a) with a front-end sales load (which
may vary among Funds), and a shareholder services fee, as described in the
Shareholder Services Agreement between the Company and William Blair (the
"Shareholder Services Agreement") (the "Front-End Load Option" or "Class A
shares"); (b) without a front-end sales load, but subject to a Contingent
Deferred Sales Charge ("CDSC"), a distribution fee, as described in the
Company's Distribution Plan for that Class, and a shareholder services fee, as
described in the Shareholder Services Agreement (the "Deferred Option" or "Class
B shares"); (c) without a front-end sales load, but subject to a CDSC, a
distribution fee, as described in the Company's Distribution Plan for that
Class, and a shareholder services fee, as described in the Shareholder Services
Agreement (the "Level Load Option" or "Class C shares"); (d) without a front-end
sales load or CDSC, but subject to a distribution fee, as described in the
Company's Distribution Plan for that Class (the "No Load Option" or "Class R
Shares"); and (e) without a front-end load, CDSC, distribution fee or
shareholder services fee ("Institutional Option" or "Class I shares"); and

         WHEREAS, Rule 18f-3 under the 1940 Act permits open-end management
investment companies to issue multiple classes of voting stock representing
interests in the same portfolio notwithstanding Sections 18(f)(1) and 18(i)
under the 1940 Act if, among other things, such investment companies adopt a
written plan setting forth the separate arrangement and expense allocation of
each class and any related conversion features or exchange privileges.

         NOW, THEREFORE, the Company, wishing to be governed by Rule 18f-3 under
the 1940 Act, hereby adopts this Multi-Class Plan as follows:

         1.  Each class of shares of each Fund will represent interests in the
same portfolio of investments of a Fund, and be identical in all respects to
each other class of a Fund, except as set forth below. The only differences
among the various classes of shares of the same Fund will relate solely to: (a)
different distribution fee payments associated with any Distribution Plan for a
particular



<PAGE>   2


class of shares and any other costs relating to implementing or amending such
Plan (including obtaining shareholder approval of such Plan or any amendment
thereto), which will be borne solely by shareholders of such classes; (b)
different shareholder services fees associated with the Shareholder Services
Agreement; and (c) different class expenses, which will be limited to any
additional expenses that are subsequently identified and determined to be
properly applied to one class of shares of a Fund upon approval by a majority of
the Directors of the Company, including a majority of the Directors who are not
interested persons of the Funds.

         2.  Under this Multi-Class Plan, certain expenses may be attributable
to a Fund, but not to a particular class thereof. All such expenses will be
borne by each class on the basis of the relative aggregate net assets of the
classes. Expenses that are attributable to a particular Fund, but not to a
particular class thereof, will be borne by each class of such series on the
basis of the relative aggregate net assets of the classes. Notwithstanding the
foregoing, the distributor, the investment manager or other provider of services
to the Company may waive or reimburse the expenses of a specific class or
classes to the extent permitted under Rule 18f-3 under the 1940 Act.

             A class of shares may be permitted to bear expenses that are
directly attributable to such class including: (a) any distribution fees
associated with the Distribution Plan for a particular class and any other costs
relating to implementing or amending such Plan (including obtaining shareholder
approval of such Plan or any amendment thereto); (b) any shareholder services
fees associated with the Shareholder Services Agreement attributable to such
class; and (d) any class expenses determined by the Directors to be attributable
to such class.

         3.  After a shareholder's Class B shares have been outstanding for
eight years, they will automatically convert to Class A shares of the same Fund
at the relative net asset values of the two classes and will thereafter not be
subject to the Distribution Plan. Class B shares issued upon reinvestment of
income and capital gain dividends and other distributions will be converted to
Class A shares on a pro rata basis with the Class B shares.

         4.  Any conversion of shares of one class to shares of another class is
subject to the continuing availability of a ruling of the Internal Revenue
Service or an opinion of counsel to the effect that the conversion of shares
does not constitute a taxable event under federal income tax law. Any such
conversion may be suspended if such a ruling or opinion is no longer available.

         5.  To the extent exchanges are permitted, shares of any class of a
Fund will be exchangeable with shares of the same class of another Fund as
described in the prospectus. Exchanges will comply with all applicable
provisions of Rule 11a-3 under the 1940 Act. For purposes of calculating the
time period remaining on the conversion of Class B shares to Class A shares,
Class B shares received on exchange retain their original purchase date.

         6.  Dividends paid by a Fund as to each class of its shares, to the
extent any dividends are paid, will be calculated in the same manner, at the
same time, on the same day, and will be in the



                                       2




<PAGE>   3


same amount, except that any distribution fees, shareholder services fees and
class expenses allocated to a class will be borne exclusively by that class.

         7.  Any distribution arrangement of a Fund, including distribution fees
and front-end and deferred sales loads, will comply with Article III, Section
26, of the Rules of Fair Practice of the National Association of Securities
Dealers, Inc.

         8.  All material amendments to this Plan must be approved by a majority
of the members of the Company's Board of Directors, including a majority of the
board members who are not interested persons of the Company.

Dated:  July 20, 1999






                                       3



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