MORGAN STANLEY DEAN WITTER HEALTH SCIENCES TRUST
497, 1998-10-08
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<PAGE>
                                                Filed Pursuant to Rule 497(e)
                                                Registration File No.: 33-48189



                             MORGAN STANLEY DEAN WITTER
                             HEALTH SCIENCES TRUST
                             PROSPECTUS -- SEPTEMBER 25, 1998
- -------------------------------------------------------------------------------

MORGAN STANLEY DEAN WITTER HEALTH SCIENCES TRUST (THE "FUND") IS AN OPEN-END,
NON-DIVERSIFIED MANAGEMENT INVESTMENT COMPANY WHOSE INVESTMENT OBJECTIVE IS
CAPITAL APPRECIATION. THE FUND SEEKS TO ACHIEVE ITS OBJECTIVE BY INVESTING IN
SECURITIES OF COMPANIES IN THE HEALTH SCIENCES INDUSTRY THROUGHOUT THE WORLD.
(SEE "INVESTMENT OBJECTIVE AND POLICIES.")




The Fund offers four classes of shares (each, a "Class"), each with a different
combination of sales charges, ongoing fees and other features. The different
distribution arrangements permit an investor to choose the method of purchasing
shares that the investor believes is most beneficial given the amount of the
purchase, the length of time the investor expects to hold the shares and other
relevant circumstances. See "Purchase of Fund Shares--Alternative Purchase
Arrangements."




This Prospectus sets forth concisely the information you should know before
investing in the Fund. It should be read and retained for future reference.
Additional information about the Fund is contained in the Statement of
Additional Information, dated September 25, 1998, which has been filed with the
Securities and Exchange Commission, and which is available at no charge upon
request of the Fund at the address or telephone numbers listed on this page.
The Statement of Additional Information is incorporated herein by reference.





TABLE OF CONTENTS

Prospectus Summary............................................    2
 
Summary of Fund Expenses......................................    4

Financial Highlights..........................................    6

The Fund and its Management...................................    8

Investment Objective and Policies.............................    8

   Risk Considerations........................................   12

Investment Restrictions.......................................   14

Purchase of Fund Shares.......................................   15

Shareholder Services..........................................   23

Redemptions and Repurchases...................................   26

Dividends, Distributions and Taxes............................   27

Performance Information.......................................   28

Additional Information........................................   28





SHARES OF THE FUND ARE NOT DEPOSITS OR OBLIGATIONS OF, OR GUARANTEED OR
ENDORSED BY, ANY BANK, AND THE SHARES ARE NOT FEDERALLY INSURED BY THE FEDERAL
DEPOSIT INSURANCE CORPORATION, THE FEDERAL RESERVE BOARD, OR ANY OTHER AGENCY.




MORGAN STANLEY DEAN WITTER
HEALTH SCIENCES TRUST
TWO WORLD TRADE CENTER
NEW YORK, NEW YORK 10048
(212) 392-2550 OR
(800) 869-NEWS (TOLL-FREE)


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 THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
 EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE SECURITIES
  AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON THE
ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS
                              A CRIMINAL OFFENSE.

           Morgan Stanley Dean Witter Distributors Inc., Distributor
<PAGE>

PROSPECTUS SUMMARY

<TABLE>
<CAPTION>
- -----------------------------------------------------------------------------------------------------------------------------------
<S>               <C>
THE               The Fund is organized as a Massachusetts business trust, and is an open-end, non-diversified
FUND              management investment company which invests in securities of companies in the health sciences
                  industry throughout the world.
- ---------------------------------------------------------------------------------------------------------------------------
SHARES OFFERED    Shares of beneficial interest with $0.01 par value (see page 28). The Fund offers four Classes of shares,
                  each with a different combination of sales charges, ongoing fees and other features (see pages 15
                  through 22).
- ----------------------------------------------------------------------------------------------------------------------------
MINIMUM           The minimum initial investment for each Class is $1,000 ($100 if the account is opened through
PURCHASE          EasyInvest(SM)). Class D shares are only available to persons investing $5 million ($25 million for
                  certain qualified plans) or more and to certain other limited categories of investors. For the purpose
                  of meeting the minimum $5 million (or $25 million) investment for Class D shares, and subject to the
                  $1,000 minimum initial investment for each Class of the Fund, an investor's existing holdings of
                  Class A shares and shares of funds for which Morgan Stanley Dean Witter Advisors Inc. serves as
                  investment manager ("Morgan Stanley Dean Witter Funds") that are sold with a front-end sales
                  charge, and concurrent investments in Class D shares of the Fund and other Morgan Stanley Dean
                  Witter Funds that are multiple class funds, will be aggregated. The minimum subsequent investment
                  is $100 (see page 15).
- -----------------------------------------------------------------------------------------------------------------------------
INVESTMENT        The investment objective of the Fund is capital appreciation (see page 8).
OBJECTIVE
- -----------------------------------------------------------------------------------------------------------------------------
INVESTMENT        The Fund will seek to achieve its investment objective by investing at least 65% of its total assets in
POLICIES          the equity securities of health science companies throughout the world. The Fund's portfolio will
                  primarily consist of common stocks, preferred stocks, convertible preferred stocks, securities
                  convertible into common stocks and warrants. The Fund may also invest in investment grade debt
                  securities when the Investment Manager believes that such securities present a favorable opportunity
                  for capital appreciation and in various other financial instruments, such as options, futures and options
                  on futures, to hedge against adverse price movements in the securities held in its portfolio, as well as
                  in the securities it might wish to purchase, and the currencies in which they are denominated (see
                  pages 8 through 12).
- ----------------------------------------------------------------------------------------------------------------------------
INVESTMENT        Morgan Stanley Dean Witter Advisors Inc. ("MSDW Advisors"), the Investment Manager of the Fund,
MANAGER           and its wholly-owned subsidiary, Morgan Stanley Dean Witter Services Company Inc., serve in various
                  investment management, advisory, management and administrative capacities to 101 investment
                  companies and other portfolios with assets of approximately $110.1 billion at August 31, 1998 (see
                  page 8).
- ----------------------------------------------------------------------------------------------------------------------------
MANAGEMENT        The Investment Manager receives a monthly fee at the annual rate of 1.0% of daily net assets, scaled
FEE               down to 0.95% on assets over $500 million (see page 8).
- ----------------------------------------------------------------------------------------------------------------------------
DISTRIBUTOR AND   Morgan Stanley Dean Witter Distributors Inc. is the Distributor of the Fund's shares. The Fund has
DISTRIBUTION      adopted a distribution plan pursuant to Rule 12b-1 under the Investment Company Act (the "12b-1
FEE               Plan") with respect to the distribution fees paid by the Class A, Class B and Class C shares of the Fund
                  to the Distributor. The entire 12b-1 fee payable by Class A and a portion of the 12b-1 fee payable by
                  each of Class B and Class C equal to 0.25% of the average daily net assets of the Class are currently
                  each characterized as a service fee within the meaning of the National Association of Securities
                  Dealers, Inc. guidelines. The remaining portion of the 12b-1 fee, if any, is characterized as an
                  asset-based sales charge (see pages 15 and 22).
- ----------------------------------------------------------------------------------------------------------------------------
ALTERNATIVE       Four classes of shares are offered:
PURCHASE
ARRANGEMENTS      o  Class A shares are offered with a front-end sales charge, starting at 5.25% and reduced for larger
                  purchases. Investments of $1 million or more (and investments by certain other limited categories of
                  investors) are not subject to any sales charge at the time of purchase but a contingent deferred sales
                  charge ("CDSC") of 1.0% may be imposed on redemptions within one year of purchase. The Fund is
                  authorized to reimburse the Distributor for specific expenses incurred in promoting the distribution
                  of the Fund's Class A shares and servicing shareholder accounts pursuant to the Fund's 12b-1 Plan.
                  Reimbursement may in no event exceed an amount equal to payments at an annual rate of 0.25% of
                  average daily net assets of the Class (see pages 15, 17 and 22).
- ----------------------------------------------------------------------------------------------------------------------------
</TABLE>

2
<PAGE>


<TABLE>
<CAPTION>
<S>             <C>
- ---------------------------------------------------------------------------------------------------------------------------
                o  Class B shares are offered without a front-end sales charge, but will in most cases be subject to a
                CDSC (scaled down from 5.0% to 1.0%) if redeemed within six years after purchase. The CDSC will
                be imposed on any redemption of shares if after such redemption the aggregate current value of a
                Class B account with the Fund falls below the aggregate amount of the investor's purchase payments
                made during the six years preceding the redemption. A different CDSC schedule applies to
                investments by certain qualified plans. Class B shares are also subject to a 12b-1 fee assessed at the
                annual rate of 1.0% of the lesser of: (a) the average daily net sales of the Fund's Class B shares or (b)
                the average daily net assets of Class B. All shares of the Fund held prior to July 28, 1997 have been
                designated Class B shares. Shares held before May 1, 1997 will convert to Class A shares in May, 2007.
                In all other instances, Class B shares convert to Class A shares approximately ten years after the date
                of the original purchase (see pages 15, 19 and 22).

                o  Class C shares are offered without a front-end sales charge, but will in most cases be subject to a
                CDSC of 1.0% if redeemed within one year after purchase. The Fund is authorized to reimburse the
                Distributor for specific expenses incurred in promoting the distribution of the Fund's Class C shares
                and servicing shareholder accounts pursuant to the Fund's 12b-1 Plan. Reimbursement may in no
                event exceed an amount equal to payments at an annual rate of 1.0% of average daily net assets of the
                Class (see pages 15, 21 and 22).

                o  Class D shares are offered only to investors meeting an initial investment minimum of $5 million
                ($25 million for certain qualified plans) and to certain other limited categories of investors. Class D
                shares are offered without a front-end sales charge or CDSC and are not subject to any 12b-1 fee (see
                pages 15, 21 and 22).
- -----------------------------------------------------------------------------------------------------------------------------
DIVIDENDS AND   Dividends from net investment income and distributions from net capital gains, if any, are paid at least
CAPITAL GAINS   annually. The Fund may, however, determine to retain all or part of any net long-term capital gains in
DISTRIBUTIONS   any year for reinvestment. Dividends and capital gains distributions paid on shares of a Class are
                automatically reinvested in additional shares of the same Class at net asset value unless the
                shareholder elects to receive cash. Shares acquired by dividend and distribution reinvestment will not
                be subject to any sales charge or CDSC (see pages 23 and 27).
- -----------------------------------------------------------------------------------------------------------------------------
REDEMPTION      Shares are redeemable by the shareholder at net asset value less any applicable CDSC on Class A,
                Class B or Class C shares. An account may be involuntarily redeemed if the total value of the account
                is less than $100 or, if the account was opened through EasyInvest(SM), if after twelve months the
                shareholder has invested less than $1,000 in the account (see page 26).
- -----------------------------------------------------------------------------------------------------------------------------
RISKS           The value of the Fund's portfolio securities, and therefore the net asset value of the Fund's shares, will
                fluctuate with changes in the market value of its portfolio securities. Unlike more widely diversified
                mutual funds, the Fund is subject to industry risk, i.e., the possibility that a particular group of related
                stocks will decline in price. In addition, the health sciences industry generally is subject to substantial
                government regulation; accordingly, changes in government policies or regulation could have a
                material effect on the demand for products and services offered by health science companies and,
                therefore, could affect the performance of the Fund. It should be recognized that the foreign securities
                and markets in which the Fund invests pose different and greater risks than those customarily
                associated with domestic securities and their markets. Furthermore, investors should consider other
                risks associated with a portfolio which contains international securities, including fluctuations in
                foreign currency exchange rates (i.e., if a substantial portion of the Fund's assets are denominated in
                foreign currencies which decrease in value with respect to the U.S. dollar, the value of the investor's
                shares and the distributions made on those shares will, likewise, decrease in value), foreign securities
                exchange controls and foreign tax rates, as well as investments in forward currency contracts, options
                and futures contracts (see pages 12 through 14).
- ----------------------------------------------------------------------------------------------------------------------------
</TABLE>

 The above is qualified in its entirety by the detailed information appearing
  elsewhere in this Prospectus and in the Statement of Additional Information.

                                                                              3
<PAGE>

SUMMARY OF FUND EXPENSES
- -------------------------------------------------------------------------------

The following table illustrates all expenses and fees that a shareholder of the
Fund will incur. The expenses and fees set forth in the table are based on the
expenses and fees for the fiscal year ended July 31, 1998.



<TABLE>
<CAPTION>
                                                                            Class A          Class B         Class C       Class D
                                                                       ----------------- --------------- --------------- ----------
<S>                                                                      <C>               <C>             <C>             <C>
SHAREHOLDER TRANSACTION EXPENSES
Maximum Sales Charge Imposed on Purchases (as a percentage of
 offering price) ............................................              5.25%(1)         None            None          None
Sales Charge Imposed on Dividend Reinvestments ..............              None             None            None          None
Maximum Contingent Deferred Sales Charge (as a percentage of
 original purchase price or redemption proceeds) ............              None(2)          5.00%(3)        1.00%(4)      None
Redemption Fees .............................................              None             None            None          None
Exchange Fee ................................................              None             None            None          None
ANNUAL FUND OPERATING EXPENSES (AS A PERCENTAGE OF AVERAGE NET ASSETS)
Management Fees (5) .........................................              1.00%            1.00%           1.00%         1.00%
12b-1 Fees (6) (7) ..........................................              0.24%            1.00%           1.00%         None
Other Expenses (5) ..........................................              0.26%            0.26%           0.26%         0.26%
Total Fund Operating Expenses ...............................              1.50%            2.26%           2.26%         1.26%
</TABLE>
- ---------
(1)   Reduced for purchases of $25,000 and over (see "Purchase of Fund
      Shares--Initial Sales Charge Alternative--Class A Shares").
(2)   Investments that are not subject to any sales charge at the time of
      purchase are subject to a CDSC of 1.00% that will be imposed on
      redemptions made within one year after purchase, except for certain
      specific circumstances (see "Purchase of Fund Shares--Initial Sales
      Charge Alternative--Class A Shares").
(3)   The CDSC is scaled down to 1.00% during the sixth year, reaching zero
      thereafter.
(4)   Only applicable to redemptions made within one year after purchase (see
      "Purchase of Fund Shares--Level Load Alternative--Class C Shares").
(5)   Management fees and other expenses are based on the Fund's actual
      aggregate expenses.
(6)   The 12b-1 fee is accrued daily and payable monthly. The entire 12b-1 fee
      payable by Class A and a portion of the 12b-1 fee payable by each of
      Class B and Class C equal to 0.25% of the average daily net assets of the
      Class are currently each characterized as a service fee within the
      meaning of National Association of Securities Dealers, Inc. ("NASD")
      guidelines and are payments made for personal service and/or maintenance
      of shareholder accounts. The remainder of the 12b-1 fee, if any, is an
      asset-based sales charge, and is a distribution fee paid to the
      Distributor to compensate it for the services provided and the expenses
      borne by the Distributor and others in the distribution of the Fund's
      shares (see "Purchase of Fund Shares--Plan of Distribution").
(7)   Upon conversion of Class B shares to Class A shares, such shares will be
      subject to the lower 12b-1 fee applicable to Class A shares. No sales
      charge is imposed at the time of conversion of Class B shares to Class A
      shares. Class C shares do not have a conversion feature and, therefore,
      are subject to an ongoing 1.00% distribution fee (see "Purchase of Fund
      Shares--Alternative Purchase Arrangements").


<TABLE>
<CAPTION>

EXAMPLES                                                                   1 Year     3 Years     5 Years     10 Years
                                                                           --------   ---------   ---------   ---------
<S>                                                                        <C>        <C>         <C>         <C> 
You would pay the following expenses on a $1,000 investment assuming (1)
a 5% annual return and (2) redemption at the end of each time period:
  Class A ..............................................................   $67        $ 97        $130        $222
  Class B ..............................................................   $73        $100        $141        $259
  Class C ..............................................................   $33        $ 70        $121        $259
  Class D ..............................................................   $13        $ 40        $ 69        $152
You would pay the following expenses on the same $1,000 investment
assuming no redemption at the end of the period:
  Class A ..............................................................   $67        $ 97        $130        $222
  Class B ..............................................................   $23        $ 70        $121        $259
  Class C ..............................................................   $23        $ 70        $121        $259
  Class D ..............................................................   $13        $ 40        $ 69        $152
</TABLE>

THE ABOVE EXAMPLES SHOULD NOT BE CONSIDERED A REPRESENTATION OF PAST OR FUTURE
EXPENSES OR PERFORMANCE. ACTUAL EXPENSES OF EACH CLASS MAY BE GREATER OR LESS
THAN THOSE SHOWN.

The purpose of this table is to assist the investor in understanding the
various costs and expenses that an investor in the Fund will bear directly or
indirectly. For a more complete description of these costs and expenses, see
"The Fund and its Management," "Purchase of Fund Shares--Plan of Distribution"
and "Redemptions and Repurchases."

Long-term shareholders of Class B and Class C may pay more in sales charges,
including distribution fees, than the economic equivalent of the maximum
front-end sales charges permitted by the NASD.

4
<PAGE>

FINANCIAL HIGHLIGHTS
- -------------------------------------------------------------------------------

The following ratios and per share data for a share of beneficial interest
outstanding throughout each period have been audited by PricewaterhouseCoopers
LLP, independent accountants. The financial highlights should be read in
conjunction with the financial statements, notes thereto and the unqualified
report of independent accountants, which are contained in the Statement of
Additional Information. Further information about the performance of the Fund
is contained in the Fund's Annual Report to Shareholders, which may be obtained
without charge upon request to the Fund.



<TABLE>
<CAPTION>
                                                                                                                  For the period
                                                                For the year ended July 31,                      October 30, 1992*
                                            -------------------------------------------------------------------       through
                                                1998++        1997**         1996         1995         1994        July 31, 1993
                                            ------------- ------------- ------------- ------------ ------------ ------------------
<S>                                         <C>           <C>           <C>           <C>          <C>          <C>
CLASS B SHARES
PER SHARE OPERATING PERFORMANCE:
 Net asset value, beginning of period .....    $  15.10      $  14.97      $  12.88      $   9.32      $   9.22      $  10.00
                                               --------      --------      --------      --------      --------      --------
 Net investment loss ......................       (0.31)        (0.31)        (0.26)        (0.24)        (0.22)        (0.08)
 
 Net realized and unrealized gain (loss)...        1.59          1.39          3.44          3.80          0.32         (0.70)
                                               --------      --------      --------      --------      --------      --------
 Total from investment operations .........        1.28          1.08          3.18          3.56          0.10         (0.78)
                                               --------      --------      --------      --------      --------      --------
 Less distributions from net realized
  gain ....................................       (1.16)        (0.95)        (1.09)           --            --            --
                                               --------      --------      --------      --------      --------      --------
 Net asset value, end of period ...........    $  15.22      $  15.10      $  14.97      $  12.88      $   9.32      $   9.22
                                               ========      ========      ========      ========      ========      ========
TOTAL INVESTMENT RETURN+ ..................        9.33 %        7.55 %       24.84 %       38.20 %        1.08 %       (7.80)%(1)
RATIOS TO AVERAGE NET ASSETS:
 Expenses .................................        2.26 %        2.25 %        2.20 %        2.30 %        2.30 %        2.38 %(2)
 Net investment loss ......................       (1.87)%       (2.08)%       (2.03)%       (2.05)%       (2.06)%       (1.38)%(2)
SUPPLEMENTAL DATA:
 Net assets, end of period, in
  thousands ...............................    $355,416      $422,667      $442,876      $273,735      $228,573      $231,646
 Portfolio turnover rate ..................         139 %          85 %          63 %         145 %         106 %          55 %(1)
</TABLE>

- ---------
*    Commencement of operations.
**   Prior to July 28, 1997, the Fund issued one class of shares. All shares of
     the Fund held prior to that date have been designated Class B shares.
++   The per share amounts were computed using an average number of shares
     outstanding during the period.
+    Does not reflect the deduction of sales charge. Calculated based on the 
     net asset value as of the last business day of the period.
(1)  Not annualized.
(2)  Annualized.


                                                                               5
<PAGE>

FINANCIAL HIGHLIGHTS--Continued
- --------------------------------------------------------------------------------


<TABLE>
<CAPTION>
                                                                             For the period
                                                          For the year       July 28, 1997*
                                                             ended               through
                                                        July 31, 1998++      July 31, 1997++
                                                       -----------------   ------------------
<S>                                                    <C>                 <C>
CLASS A SHARES
PER SHARE OPERATING PERFORMANCE:
 Net asset value, beginning of period ..............    $ 15.10                 $ 15.03
                                                        -------                 -------
 Net investment loss ...............................      (0.18)                     --
 Net realized and unrealized gain ..................       1.55                    0.07
                                                        -------                 -------
 Total from investment operations ..................       1.37                    0.07
                                                        -------                 -------
 Less distributions from net realized gain .........      (1.16)                     --
                                                        -------                 -------
 Net asset value, end of period ....................    $ 15.31                 $ 15.10
                                                        =======                 =======
TOTAL INVESTMENT RETURN+ ...........................       9.94 %                  0.47 %(1)
RATIOS TO AVERAGE NET ASSETS:
 Expenses ..........................................       1.51 %                  1.57 %(2)
 Net investment loss ...............................      (1.06)%                 (0.55)%(2)
SUPPLEMENTAL DATA:
 Net assets, end of period, in thousands ...........       $260                     $10
 Portfolio turnover rate ...........................        139 %                    85 %
CLASS C SHARES
PER SHARE OPERATING PERFORMANCE:
 Net asset value, beginning of period ..............    $ 15.10                 $ 15.03
                                                       --------            ------------
 Net investment loss ...............................      (0.29)                     --
 Net realized and unrealized gain ..................       1.58                    0.07
                                                       --------            ------------
 Total from investment operations ..................       1.29                    0.07
                                                       --------            ------------
 Less distributions from net realized gain .........      (1.16)                     --
                                                       --------            ------------
 Net asset value, end of period ....................    $ 15.23                 $ 15.10
                                                       ========            ============
TOTAL INVESTMENT RETURN+ ...........................       9.40 %                  0.47 %(1)
RATIOS TO AVERAGE NET ASSETS:
 Expenses ..........................................       2.27 %                  2.31 %(2)
 Net investment loss ...............................      (1.78)%                 (1.28)%(2)
SUPPLEMENTAL DATA:
 Net assets, end of period, in thousands ...........       $485                     $20
 Portfolio turnover rate ...........................        139 %                    85 %
</TABLE>

- ---------
*    The date shares were first issued.
++   The per share amounts were computed using an average number of shares
     outstanding during the period.
+    Does not reflect the deduction of sales charge. Calculated based on the 
     net asset value as of the last business day of the period.
(1)  Not annualized.
(2)  Annualized.

6
<PAGE>

FINANCIAL HIGHLIGHTS--Continued
- --------------------------------------------------------------------------------


<TABLE>
<CAPTION>
                                                                             For the period
                                                          For the year       July 28, 1997*
                                                             ended               through
                                                        July 31, 1998++      July 31, 1997++
                                                       -----------------   ------------------
<S>                                                    <C>                 <C>
CLASS D SHARES
PER SHARE OPERATING PERFORMANCE:
 Net asset value, beginning of period ..............    $ 15.10                 $ 15.03
                                                        -------                 -------
 Net investment loss ...............................      (0.14)                     --
 Net realized and unrealized gain ..................       1.55                    0.07
                                                        -------                 -------
 Total from investment operations ..................       1.41                    0.07
                                                        -------                 -------
 Less distributions from net realized gain .........      (1.16)                      --
                                                        -------                 -------
 Net asset value, end of period ....................    $ 15.35                 $ 15.10
                                                        =======                 =======
TOTAL INVESTMENT RETURN+ ...........................      10.22 %                  0.47 %(1)
RATIOS TO AVERAGE NET ASSETS:
 Expenses ..........................................       1.26 %                  1.31 %(2)
 Net investment loss ...............................      (0.79)%                 (0.29)%(2)
SUPPLEMENTAL DATA:
 Net assets, end of period, in thousands ...........     $1,244                     $10
 Portfolio turnover rate ...........................        139 %                    85 %
</TABLE>

- ---------
*    The date shares were first issued.
++   The per share amounts were computed using an average number of shares
     outstanding during the period.
+    Does not reflect the deduction of sales charge. Calculated based on the 
     net asset value as of the last business day of the period.
(1)  Not annualized.
(2)  Annualized.


                                                                              7
<PAGE>

THE FUND AND ITS MANAGEMENT
- -------------------------------------------------------------------------------

Morgan Stanley Dean Witter Health Sciences Trust (formerly named Dean Witter
Health Sciences Trust) (the "Fund") is an open-end, non-diversified management
investment company. The Fund is a trust of the type commonly known as a
"Massachusetts business trust" and was organized under the laws of The
Commonwealth of Massachusetts on May 26, 1992.

      Morgan Stanley Dean Witter Advisors Inc. ("MSDW Advisors" or the
"Investment Manager"), whose address is Two World Trade Center, New York, New
York 10048, is the Fund's Investment Manager. The Investment Manager is a
wholly-owned subsidiary of Morgan Stanley Dean Witter & Co., a preeminent
global financial services firm that maintains leading market positions in each
of its three primary businesses--securities, asset management and credit
services. The Investment Manager, which was incorporated in July, 1992 under
the name Dean Witter InterCapital Inc., changed its name to Morgan Stanley Dean
Witter Advisors Inc. on June 22, 1998.

      MSDW Advisors and its wholly-owned subsidiary, Morgan Stanley Dean Witter
Services Company Inc. ("MSDW Services"), serve in various investment
management, advisory, management and administrative capacities to 101
investment companies, 28 of which are listed on the New York Stock Exchange,
with combined assets of approximately $106 billion at August 31, 1998. The
Investment Manager also manages portfolios of pension plans, other institutions
and individuals which aggregated approximately $4.1 billion at such date.

      The Fund has retained the Investment Manager, pursuant to an Investment
Management Agreement, to provide administrative services, manage its business
affairs and manage the investment of the Fund's assets, including the placing
of orders for the purchase and sale of portfolio securities. MSDW Advisors has
retained MSDW Services to perform the aforementioned administrative services
for the Fund.


      The Fund's Board of Trustees reviews the various services provided by or
under the direction of the Investment Manager to ensure that the Fund's general
investment policies and programs are being properly carried out and that
administrative services are being provided to the Fund in a satisfactory
manner.


      As full compensation for the services and facilities furnished to the
Fund and for expenses of the Fund assumed by the Investment Manager, the Fund
pays the Investment Manager monthly compensation calculated daily by applying
the annual rate of 1.0% of the daily net assets up to $500 million, scaled down
to 0.95% on assets over $500 million, determined as of the close of each
business day. For the fiscal year ended July 31, 1998, the Fund accrued total
compensation to the Investment Manager amounting to 1.0% of the Fund's daily
net assets and the total expenses of each Class amounted to 1.51%, 2.26%, 2.27%
and 1.26% of the average daily net assets of Class A, Class B, Class C and
Class D, respectively.

INVESTMENT OBJECTIVE AND POLICIES
- -------------------------------------------------------------------------------

The investment objective of the Fund is capital appreciation. The investment
objective of the Fund is a fundamental policy and may not be changed without
the approval of the holders of a majority of the Fund's shares. There is no
assurance that the Fund's investment objective will be achieved.


      The Fund will seek to achieve its investment objective by investing at
least 65% of its total assets in the equity securities of health science
companies throughout the world. A health science company is defined as a
company which is principally engaged in the health sciences industry. A company
is deemed to be "principally engaged" if it has at least 50% of its earnings or
revenues derived from health sciences activities, as defined below, or at least
50% of its assets is devoted to such activities, based upon the financial
statements of the company's most recently reported fiscal year.

      In addition, the Investment Manager may invest in companies other than
health science companies if it considers that such companies have potential for
capital appreciation primarily as a result of particular products, technology,
patents or other market advantages in the health sciences industry. The Fund
does not anticipate that companies not principally engaged in the health
sciences industry will represent more than 20% of the Fund's investments.

      Health sciences activities are defined as activities which consist of the
research, development, production or distribution of products and services by
health science companies which include, but are not limited to, companies such
as: pharmaceutical companies; companies involved in the ownership and/or
operation or delivery of health care services such as hospitals, clinical test
laboratories, convalescent and mental health care facilities, rehabilitation
centers, and products and services for


8
<PAGE>

home care; companies involved in biotechnology, medical diagnostics,
biochemical, and nuclear research and development; and companies that produce
and manufacture medical, dental and optical supplies and equipment.

      The Fund's portfolio will primarily consist of common stocks. The Fund
may also invest up to 35% of its total assets in preferred stock and in
investment grade domestic and foreign debt securities of any type of issuer
(such as foreign and domestic corporations and foreign and domestic governments
and their political subdivisions), including bonds, notes, debentures and debt
securities convertible into equity if the Investment Manager believes that such
securities present a favorable opportunity for capital appreciation. The term
investment grade consists of debt instruments rated Baa or higher by Moody's
Investors Service, Inc. ("Moody's") or BBB or higher by Standard & Poor's
Corporation ("S&P") or, if not rated, determined to be of comparable quality by
the Investment Manager. Investments in securities rated either Baa by Moody's
or BBB by S&P may have speculative characteristics and, therefore, changes in
economic conditions or other circumstances are more likely to weaken their
capacity to make principal and interest payments than would be the case with
investments in securities with higher credit ratings. If a debt instrument held
by the Fund is rated BBB or Baa and is subsequently downgraded by a rating
agency, the Fund will retain such security in its portfolio until the
Investment Manager determines that it is practicable to sell the security
without undue market or tax consequences to the Fund. In the event that such
downgraded securities constitute 5% or more of the Fund's total assets, the
Investment Manager will sell immediately sufficient securities to reduce the
total to below 5%. The Fund may invest in various other financial instruments
such as warrants and forward foreign currency exchange contracts, futures and
options, including stock index futures contracts and related options in an
attempt to hedge its portfolio (see below).

FOREIGN SECURITIES. While the Fund expects that, from time to time, a
significant portion of its investments will be in securities of U.S. companies,
the Fund's Investment Manager believes that a portfolio comprised only of U.S.
securities does not provide the greatest potential for capital appreciation
from an investment in the health sciences industry. It believes that a
worldwide focus is necessary if the Fund is to take advantage of the increasing
opportunities presented by health science companies headquartered throughout
the world. The Fund may invest substantially in securities denominated in one
or more currencies. The Investment Manager believes that by investing
worldwide, the Fund can better position itself to take advantage of available
health sciences investment opportunities (see "Risk Considerations").

      Many European countries are about to adopt a single European currency,
the euro ("the Euro Conversion"). The consequences of the Euro Conversion for
foreign exchange rates, interest rates and the value of European securities
eligible for purchase by the Fund are presently unclear. Such consequences may
adversely affect the value and/or increase the volatility of securities held by
the Fund.

      The Fund may also invest in securities of foreign issuers in the form of
American Depository Receipts (ADRs), European Depository Receipts (EDRs) or
other similar 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. ADRs are receipts typically issued
by a United States bank or trust company evidencing ownership of the underlying
securities. EDRs are European receipts evidencing a similar arrangement.
Generally, ADRs, in registered form, are designed for use in the United States
securities markets and EDRs, in bearer form, are designed for use in European
securities markets.

PRIVATE PLACEMENTS/ILLIQUID SECURITIES. The Fund may invest up to 5% of its
total assets in securities that are subject to restrictions on resale (referred
to as private placements or restricted securities) because they have not been
registered under the Securities Act of 1933, as amended, or which are otherwise
not readily marketable. (Securities eligible for resale pursuant to Rule 144A
of the Securities Act, and determined to be liquid pursuant to the procedures
adopted by the Board of Trustees, are not subject to the foregoing
restriction.) If a restricted security is determined to be "liquid," such
security will not be included within the category "illiquid securities," which
is limited by the Fund's investment policies to 15% of the Fund's net assets.
Investing in Rule 144A securities could have the effect of increasing the level
of Fund illiquidity to the extent the Fund, at a particular point in time, may
be unable to find qualified institutional buyers interested in purchasing such
securities. Generally, OTC options and the assets used as "cover" for written
OTC options are illiquid securities. However, the Fund is permitted to treat
the securities it uses as cover for written OTC options as liquid provided it
follows a procedure whereby it will sell OTC options only to qualified dealers
who agree that the Fund may repurchase such options at a maximum price to be
calculated pursuant to a predetermined formula set forth in the option
agreement. See "Investment Practices and Policies" in the Statement of
Additional Information.


                                                                              9
<PAGE>

      There may be periods during which market conditions warrant reduction of
some or all of the Fund's securities holdings. During such periods, the Fund
may adopt a temporary "defensive" posture in which greater than 35% of its
total assets are invested in cash (U.S. dollars, foreign currencies or
multinational currency units) and/or invest any portion of its assets in high
quality debt securities or money market instruments of U.S. or foreign issuers.
Under such circumstances, the money market instruments in which the Fund may
invest are securities issued or guaranteed by U.S. or foreign governments;
American bank obligations; Eurodollar certificates of deposit; obligations of
American savings institutions; fully insured certificates of deposit; and
commercial paper of American issuers rated within the two highest grades by
Moody's or S&P or, if not rated, are issued by a company having an outstanding
debt issue rated at least AA by S&P or Aa by Moody's.

      The Fund is classified as a non-diversified investment company under the
Investment Company Act of 1940, as amended (the "Act"), and as such is not
limited by the Act in the proportion of its assets that it may invest in the
obligations of a single issuer. However, the Fund intends to conduct its
operations so as to qualify as a "regulated investment company" under
Subchapter M of the Internal Revenue Code. See "Dividends, Distributions and
Taxes." In order to qualify, among other requirements, the Fund will limit its
investments so that at the close of each quarter of the taxable year, (i) not
more than 25% of the market value of the Fund's total assets will be invested
in the securities of a single issuer, and (ii) with respect to 50% of the
market value of its total assets, not more than 5% will be invested in the
securities of a single issuer and the Fund will not own more than 10% of the
outstanding voting securities of a single issuer. To the extent that a
relatively high percentage of the Fund's assets may be invested in the
securities of a limited number of issuers, the Fund's portfolio securities may
be more susceptible to any single economic, political or regulatory occurrence
than the portfolio securities of a diversified investment company. The
limitations described in this paragraph are not fundamental policies and may be
revised to the extent applicable Federal income tax requirements are revised.




FORWARD FOREIGN CURRENCY EXCHANGE CONTRACTS

A forward foreign currency exchange contract ("forward contract") involves an
obligation to purchase or sell a currency at a future date, which may be any
fixed number of days from the date of the contract agreed upon by the parties,
at a price set at the time of the contract. The Fund may enter into forward
contracts as a hedge against fluctuations in future foreign exchange rates.

      The Fund will enter into forward contracts under various circumstances.
When the Fund enters into a contract for the purchase or sale of a security
denominated in a foreign currency, it may, for example, desire to "lock in" the
price of the security in U.S. dollars or some other foreign currency which the
Fund is temporarily holding in its portfolio. At other times, when, for
example, it is believed that the currency of a particular foreign country may
suffer a substantial decline against the U.S. dollar or some other foreign
currency, the Fund may enter into a forward contract to sell, for a fixed
amount of dollars or other currency, the amount of foreign currency
approximating the value of some or all of the Fund's portfolio securities (or
securities which the Fund has purchased for its portfolio) denominated in such
foreign currency. Under identical circumstances, the Fund may enter into a
forward contract to sell, for a fixed amount of U.S. dollars or other currency,
an amount of foreign currency other than the currency in which the securities
to be hedged are denominated approximating the value of some or all of the
portfolio securities to be hedged. This method of hedging, called
"cross-hedging," will be selected when it is determined that the foreign
currency in which the portfolio securities are denominated has insufficient
liquidity or is trading at a discount as compared with some other foreign
currency with which it tends to move in tandem.

      In addition, when the Fund anticipates purchasing securities at some time
in the future, and wishes to lock in the current exchange rate of the currency
in which those securities are denominated against the U.S. dollar or some other
foreign currency, it may enter into a forward contract to purchase an amount of
currency equal to some or all of the value of the anticipated purchase, for a
fixed amount of U.S. dollars or other currency. Lastly, the Fund is permitted
to enter into forward contracts with respect to currencies in which certain of
its portfolio securities are denominated and on which options have been written
(see "Options and Futures Transactions").



OPTIONS AND FUTURES TRANSACTIONS

Call and put options on U.S. Treasury notes, bonds and bills, on various
foreign currencies and on equity securities are listed on several U.S. and
foreign securities exchanges and are written in over-the-counter transactions
("OTC options"). Listed options are issued or guaranteed by the exchange on
which they trade or by a clearing corporation such as the Options Clearing
Corporation ("OCC"). Ownership of a listed call option gives


10
<PAGE>

the Fund the right to buy from the OCC (in the U.S.) or other clearing
corporation or exchange, the underlying security or currency covered by the
option at the stated exercise price (the price per unit of the underlying
security or currency) by filing an exercise notice prior to the expiration date
of the option. The writer (seller) of the option would then have the obligation
to sell, to the OCC (in the U.S.) or other clearing corporation or exchange,
the underlying security or currency at that exercise price prior to the
expiration date of the option, regardless of its then current market price.
Ownership of a listed put option would give the Fund the right to sell the
underlying security or currency to the OCC (in the U.S.) or other clearing
corporation or exchange at the stated exercise price. Upon notice of exercise
of the put option, the writer of the option would have the obligation to
purchase the underlying security or currency from the OCC (in the U.S.) or
other clearing corporation or exchange at the exercise price.

FUTURES CONTRACTS. The Fund may purchase and sell futures contracts that are
currently traded, or may in the future be traded, on U.S. and foreign commodity
exchanges on common stocks, such underlying fixed-income securities as U.S.
Treasury bonds, notes, and bills and/or any foreign government fixed-income
security ("interest rate" futures), on various currencies ("currency" futures)
and on such indexes of U.S. or foreign equity and fixed-income securities as
may exist or come into being, such as the Standard & Poor's 500 Index or the
Financial Times Equity Index ("index" futures). As a futures contract
purchaser, the Fund incurs an obligation to take delivery of a specified amount
of the obligation underlying the contract at a specified time in the future for
a specified price. As a seller of a futures contract, the Fund incurs an
obligation to deliver the specified amount of the underlying obligation at a
specified time in return for an agreed upon price.

OPTIONS ON FUTURES CONTRACTS. The Fund may purchase and write call and put
options on futures contracts which are traded on an exchange and enter into
closing transactions with respect to such options to terminate an existing
position.



OTHER INVESTMENT POLICIES

REPURCHASE AGREEMENTS. The Fund may enter into repurchase agreements, which may
be viewed as a type of secured lending by the Fund, and which typically involve
the acquisition by the Fund of debt securities, from a selling financial
institution such as a bank, savings and loan association or broker-dealer. The
agreement provides that the Fund will sell back to the institution, and that
the institution will repurchase, the underlying security at a specified price
and at a fixed time in the future, usually not more than seven days from the
date of purchase. While repurchase agreements involve certain risks not
associated with direct investments in debt securities, including the risks of
default or bankruptcy of the selling financial institution, the Fund follows
procedures designed to minimize such risks. These procedures include effecting
repurchase transactions only with large, well-capitalized and well-established
financial institutions and maintaining adequate collateralization.

WHEN-ISSUED AND DELAYED DELIVERY SECURITIES AND FORWARD COMMITMENTS. From time
to time, in the ordinary course of business, the Fund may purchase securities
on a when-issued or delayed delivery basis or may purchase or sell securities
on a forward commitment basis. When such transactions are negotiated, the price
is fixed at the time of the commitment, but delivery and payment can take place
a month or more after the date of the commitment. There is no overall limit on
the percentage of the Fund's assets which may be committed to the purchase of
securities on a when-issued, delayed delivery, or forward commitment basis. An
increase in the percentage of the Fund's assets committed to the purchase of
securities on a when-issued, delayed delivery, or forward commitment basis may
increase the volatility of the Fund's net asset value.

WHEN, AS AND IF ISSUED SECURITIES. The Fund may purchase securities on a "when,
as and if issued" basis under which the issuance of the security depends upon
the occurrence of a subsequent event, such as approval of a merger, corporate
reorganization, leveraged buyout or debt restructuring. If the anticipated
event does not occur and the securities are not issued, the Fund will have lost
an investment opportunity. There is no overall limit on the percentage of the
Fund's assets which may be committed to the purchase of securities on a "when,
as and if issued" basis. An increase in the percentage of the Fund's assets
committed to the purchase of securities on a "when, as and if issued" basis may
increase the volatility of its net asset value.

LENDING OF PORTFOLIO SECURITIES. Consistent with applicable regulatory
requirements, the Fund may lend its portfolio securities to brokers, dealers
and other financial institutions, provided that such loans are callable at any
time by the Fund (subject to certain notice provisions described in the
Statement of Additional Information), and are at all times secured by cash or
cash equivalents, which are maintained in a segregated account pursuant to
applicable regulations and that are at least equal to the market value,
determined daily, of the loaned securities.

      Except as specifically noted, all investment objectives, policies and
practices discussed above are not


                                                                             11
<PAGE>

fundamental policies of the Fund and, as such, may be changed without
shareholder approval.




PORTFOLIO MANAGEMENT

The Fund's portfolio is actively managed by its Investment Manager with a view
to achieving the Fund's investment objective. In determining which securities
to purchase for the Fund or hold in the Fund's portfolio, the Investment
Manager will rely on information from various sources, including research,
analysis and appraisals of brokers and dealers, including Dean Witter Reynolds
Inc., Morgan Stanley & Co. Incorporated and other broker-dealers that are
affiliates of the Investment Manager, and the Investment Manager's own analysis
of factors they deem relevant. The Fund's portfolio is managed within MSDW
Advisors' Growth Group, which manages 32 funds and fund portfolios, with
approximately $11 billion in assets as of August 31, 1998. Ronald J. Worobel,
Senior Vice President of MSDW Advisors and a member of MSDW Advisors' Growth
Group, has been the primary portfolio manager since the Fund's inception and
has been assisted by Teresa McRoberts since July 1998. Mr. Worobel has been a
portfolio manager at MSDW Advisors for over five years. Ms. McRoberts has been
a portfolio manager at MSDW Advisors since July 1, 1998, prior thereto she was
employed at Fred Alger Management, Inc. (July 1994-May 1998) and prior thereto
she was employed at J.P. Morgan & Co. ( July 1985 -July 1994).

      Personnel of the Investment Manager have substantial experience in the
use of the investment techniques described above under the heading "Options and
Futures Transactions," which techniques require skills different from those
needed to select the portfolio securities underlying various options and
futures contracts.

      Pursuant to an order of the Securities and Exchange Commission, the Fund
may effect principal transactions in certain money market instruments with Dean
Witter Reynolds Inc. In addition, the Fund may incur brokerage commissions on
transactions conducted through Dean Witter Reynolds Inc., Morgan Stanley & Co.
Incorporated and other brokers and dealers that are affiliates of MSDW
Advisors.

      It is not anticipated that the Fund's portfolio turnover rate will exceed
100% in any one year. Short-term gains and losses taxable at ordinary income
rates may result from such portfolio transactions. See "Dividends,
Distributions and Taxes" for a full discussion of the tax implications of the
Fund's trading policy. A more extensive discussion of the Fund's portfolio
brokerage policies is set forth in the Statement of Additional Information.

      The expenses of the Fund relating to its portfolio management are likely
to be greater than those incurred by other investment companies investing
primarily in securities issued by domestic issuers as custodial costs,
brokerage commissions and other transaction charges related to investing on
foreign markets are generally higher than in the United States.




RISK CONSIDERATIONS

The net asset value of the Fund's shares will fluctuate with changes in the
market value of its portfolio securities. Dividends payable by the Fund will
vary in relation to the amount of income earned on portfolio securities.

HEALTH SCIENCES INDUSTRY. Investors should consider that the assets of the Fund
are subject to "industry risk" because investments will be concentrated in a
particular group of related stocks. The concentration of investments in the
health sciences industry may cause the value of the Fund's shares to fluctuate
more widely than those funds investing in a greater variety of industries. The
Investment Manager believes, however, that the Fund's concentration of
investments in the health sciences industry also may provide it with the
potential to achieve greater long-term performance than investments in a
variety of industries. In addition, the health sciences industry generally is
subject to substantial government regulation; accordingly, changes in
government policies or regulation could have a material effect on the demand
for products and services offered by health science companies, thereby
affecting the performance of the Fund. In addition, the products and services
offered by such companies may be subject to rapid obsolescence caused by
technological and scientific advances.

      While the Fund's portfolio normally will include securities of
established suppliers of traditional products and services, the Fund may invest
in smaller companies which can benefit from the development of new products and
services. These smaller companies may present greater opportunities for capital
appreciation, but may also involve greater risks, than large, established
issuers. Such smaller companies may have limited product lines, markets or
financial resources, and their securities may trade less frequently and in more
limited volume than the securities of larger, more established companies. As a
result, the prices of the securities of such smaller companies may fluctuate to
a greater degree than the prices of the securities of other issuers.

FOREIGN SECURITIES. Investors should carefully consider the risks of the Fund's
investing in securities of foreign issuers and securities denominated in
non-U.S.


12
<PAGE>

currencies. Fluctuations in the relative rates of exchange between different
currencies will affect the value of the Fund's investments. Changes in foreign
currency exchange rates relative to the U.S. dollar will affect the U.S. dollar
value of the Fund's assets denominated in that currency and may thereby
adversely impact upon the Fund's total return on such assets.

      Foreign currency exchange rates are determined by forces of supply and
demand on the foreign exchange markets. These forces are themselves affected by
the international balance of payments and other economic and financial
conditions, government intervention, speculation and other factors. Moreover,
foreign currency exchange rates may be affected by the regulatory control of
the exchanges on which the currencies trade. The foreign currency transactions
of the Fund will be conducted on a spot basis or through forward contracts or
futures contracts (see below). The Fund may incur certain costs in connection
with these currency transactions.

      Investments in foreign securities will also occasion risks relating to
political and economic developments abroad, including the possibility of
expropriations or confiscatory taxation, limitations on the use or transfer of
Fund assets and any effects of foreign social, economic or political
instability. Political and economic developments in Europe, especially as they
relate to changes in the structure of the European Economic Community and the
anticipated development of a unified common market, may have profound effects
upon the value of a large segment of the Fund's portfolio. Continued progress
in the evolution of, for example, a united European common market may be slowed
by unanticipated political or social events and may, therefore, adversely
affect the value of certain of the securities held in the Fund's portfolio.
Foreign companies are not subject to the regulatory requirements of U.S.
companies and, are subject to different risks relating to claims and
litigation. Regulation of the health sciences industry in foreign countries is
different from that in the U.S. and there are differences in environmental and
securities regulation. There is less publicly available information about
foreign companies as well. Moreover, foreign companies are not subject to
uniform accounting, auditing and financial reporting standards and requirements
comparable to those applicable to U.S. companies.

      The price changes of securities of foreign issuers may be more volatile
than comparable securities of U.S. issuers. Furthermore, foreign exchanges and
broker-dealers are generally subject to less government and exchange scrutiny
and regulation than their American counterparts. Brokerage commissions, dealer
concessions and other transaction costs may be higher on foreign markets than
in the U.S. In addition, differences in clearance and settlement procedures on
foreign markets may occasion delays in settlements of Fund trades effected in
such markets. Inability to dispose of portfolio securities due to settlement
delays could result in losses to the Fund due to subsequent declines in value
of such securities and the inability of the Fund to make intended security
purchases due to settlement problems could result in a failure of the Fund to
make potentially advantageous investments.

      To hedge against adverse price movements in the securities held in its
portfolio and the currencies in which they are denominated (as well as in the
securities it might wish to purchase and their denominated currencies) the Fund
may engage in transactions in forward foreign currency contracts, options on
securities and currencies, and futures contracts and options on futures
contracts on securities, currencies and indexes. The Fund may also purchase
options on securities to facilitate its participation in the potential
appreciation of the value of the underlying securities. A discussion of these
transactions follows and is supplemented by further disclosure in the Statement
of Additional Information.

FORWARD FOREIGN CURRENCY EXCHANGE CONTRACTS. If the currency in which the
Fund's portfolio securities (or anticipated portfolio securities) are
denominated rises in value with respect to the currency which is being
purchased (or sold), then the Fund will have realized fewer gains than had the
Fund not entered into the forward contracts. Moreover, the precise matching of
the forward contract amounts and the value of the securities involved will not
generally be possible, since the future value of such securities in foreign
currencies will change as a consequence of market movements in the value of
those securities between the date the forward contract is entered into and the
date it matures. The Fund is not required to enter into such transactions with
regard to its foreign currency-denominated securities and will not do so unless
deemed appropriate by the Investment Manager.

OPTIONS AND FUTURES TRANSACTIONS. The Fund may close out its position as writer
of an option, or as a buyer or seller of a futures contract, only if a liquid
secondary market exists for options or futures contracts of that series. There
is no assurance that such a market will exist, particularly in the case of OTC
options, as such options will generally only be closed out by entering into a
closing purchase transaction with the purchasing dealer.

      While the futures contracts and options transactions to be engaged in by
the Fund for the purpose of hedging the Fund's portfolio securities are not
speculative in nature, there are risks inherent in the use of such


                                                                             13
<PAGE>

instruments. One such risk is that the Fund's management could be incorrect in
its expectations as to the direction or extent of various interest rate or
price movements or the time span within which the movements take place. For
example, if the Fund sold futures contracts for the sale of securities in
anticipation of an increase in interest rates, and then interest rates went
down instead, causing bond prices to rise, the Fund would lose money on the
sale.

      Another risk which may arise in employing futures contracts to protect
against the price volatility of portfolio securities is that the prices of
securities, currencies and indices subject to futures contracts (and thereby
the futures contract prices) may correlate imperfectly with the behavior of the
U.S. dollar cash prices of the Fund's portfolio securities and their
denominated currencies. Another such risk is that prices of interest rate
futures contracts may not move in tandem with the changes in prevailing
interest rates against which the Fund seeks a hedge. A correlation may also be
distorted by the fact that the futures market is dominated by short-term
traders seeking to profit from the difference between a contract or security
price objective and their cost of borrowed funds. Such distortions are
generally minor and would diminish as the contract approached maturity.

YEAR 2000.  The investment management services provided to the Fund by the
Investment Manager and the services provided to shareholders by the Distributor
and the Transfer Agent depend on the smooth functioning of their computer
systems. Many computer software systems in use today cannot recognize the year
2000, but revert to 1900 or some other date, due to the manner in which dates
were encoded and calculated. That failure could have a negative impact on the
handling of securities trades, pricing and account services. The Investment
Manager, the Distributor and the Transfer Agent have been actively working on
necessary changes to their own computer systems to prepare for the year 2000
and expect that their systems will be adapted before that date, but there can
be no assurance that they will be successful, or that interaction with other
non-complying computer systems will not impair their services at that time.

      In addition, it is possible that the markets for securities in which the
Fund invests may be detrimentally affected by computer failures throughout the
financial services industry beginning January 1, 2000. Improperly functioning
trading systems may result in settlement problems and liquidity issues. In
addition, corporate and governmental data processing errors may result in
production problems for individual companies and overall economic
uncertainties. Earnings of individual issuers will be affected by remediation
costs, which may be substantial and may be reported inconsistently in U.S. and
foreign financial statements. Accordingly, the Fund's investments may be
adversely affected.

      For additional risk disclosure, please refer to the "Investment Objective
and Policies" section of the Prospectus and to the "Investment Practices and
Policies" section in the Statement of Additional Information.

INVESTMENT RESTRICTIONS
- -------------------------------------------------------------------------------

The investment restrictions listed below are among the restrictions which have
been adopted by the Fund as fundamental policies. Under the Investment Company
Act of 1940, as amended (the "Act"), a fundamental policy may not be changed
without the vote of a majority of the outstanding voting securities of the
Fund, as defined in the Act. For purposes of the following limitations: (i) all
percentage limitations apply immediately after a purchase or initial
investment, and (ii) any subsequent change in any applicable percentage
resulting from market fluctuations or other changes in total or net assets does
not require elimination of any security from the portfolio.

      The Fund may not:

      1. Invest 25% or more of the value of its total assets in securities of
issuers in any one industry, except the Fund will invest at least 25% of the
value of its total assets in the health sciences industry.

      2. Invest more than 5% of the value of its total assets in securities of
issuers having a record, together with predecessors, of less than three years
of continuous operation. This restriction shall not apply to any obligation
issued or guaranteed by the United States Government, its agencies or
instrumentalities.


      3. Purchase or sell commodities or commodities contracts except that the
Fund may purchase or write interest rate, currency and stock and bond index
futures contracts and related options thereon.


      4. Pledge its assets or assign or otherwise encumber them except to
secure permitted borrowings. (For the purpose of this restriction, collateral
arrangements with respect to the writing of options and collateral arrangements
with respect to initial or variation margin for futures are not deemed to be
pledges of assets.)


14
<PAGE>

      5. Purchase securities on margin (but the Fund may obtain short-term
loans as are necessary for the clearance of transactions). The deposit or
payment by the Fund of initial or variation margin in connection with futures
contracts or related options thereon is not considered the purchase of a
security on margin.

      Notwithstanding any other investment policy or restriction, the Fund may
seek to achieve its investment objective by investing all or substantially all
of its assets in another investment company having substantially the same
investment objective and policies as the Fund.

PURCHASE OF FUND SHARES
- -------------------------------------------------------------------------------

GENERAL


The Fund offers each Class of its shares for sale to the public on a continuous
basis. Pursuant to a Distribution Agreement between the Fund and Morgan Stanley
Dean Witter Distributors Inc. ("MSDW Distributors" or the "Distributor"), an
affiliate of the Investment Manager, shares of the Fund are distributed by the
Distributor and offered by Dean Witter Reynolds Inc. ("DWR"), a selected dealer
and subsidiary of Morgan Stanley Dean Witter & Co., and other dealers which
have entered into Selected Dealers Agreements with the Distributor ("Selected
Broker-Dealers"). It is anticipated that DWR will undergo a change of corporate
name which is expected to incorporate the brand name of "Morgan Stanley Dean
Witter," pending approval of various regulatory authorities. The principal
executive office of the Distributor is located at Two World Trade Center, New
York, New York 10048.

      The Fund offers four classes of shares (each, a "Class"). Class A shares
are sold to investors with an initial sales charge that declines to zero for
larger purchases; however, Class A shares sold without an initial sales charge
are subject to a contingent deferred sales charge ("CDSC") of 1.0% if redeemed
within one year of purchase, except for certain specific circumstances. Class B
shares are sold without an initial sales charge but are subject to a CDSC
(scaled down from 5.0% to 1.0%) payable upon most redemptions within six years
after purchase. (Class B shares purchased by certain qualified plans are
subject to a CDSC scaled down from 2.0% to 1.0% if redeemed within three years
after purchase.) Class C shares are sold without an initial sales charge but
are subject to a CDSC of 1.0% on most redemptions made within one year after
purchase. Class D shares are sold without an initial sales charge or CDSC and
are available only to investors meeting an initial investment minimum of $5
million ($25 million for certain qualified plans), and to certain other limited
categories of investors. At the discretion of the Board of Trustees of the
Fund, Class A shares may be sold to categories of investors in addition to
those set forth in this prospectus at net asset value without a front-end sales
charge, and Class D shares may be sold to certain other categories of
investors, in each case as may be described in the then current prospectus of
the Fund. See "Alternative Purchase Arrangements--Selecting a Particular Class"
for a discussion of factors to consider in selecting which Class of shares to
purchase.

      The minimum initial purchase is $1,000 for each Class of shares, although
Class D shares are only available to persons investing $5 million ($25 million
for certain qualified plans), or more and to certain other limited categories
of investors. For the purpose of meeting the minimum $5 million (or $25
million) initial investment for Class D shares, and subject to the $1,000
minimum initial investment for each Class of the Fund, an investor's existing
holdings of Class A shares of the Fund and other Morgan Stanley Dean Witter
Funds that are multiple class funds ("Morgan Stanley Dean Witter Multi-Class
Funds") and shares of Morgan Stanley Dean Witter Funds sold with a front-end
sales charge ("FSC Funds") and concurrent investments in Class D shares of the
Fund and other Morgan Stanley Dean Witter Multi-Class Funds will be aggregated.
Subsequent purchases of $100 or more may be made by sending a check, payable to
Morgan Stanley Dean Witter Health Sciences Trust, directly to Morgan Stanley
Dean Witter Trust FSB (the "Transfer Agent" or "MSDW Trust") at P.O. Box 1040,
Jersey City, NJ 07303 or by contacting a Morgan Stanley Dean Witter Financial
Advisor or other Selected Broker-Dealer representative. When purchasing shares
of the Fund, investors must specify whether the purchase is for Class A, Class
B, Class C or Class D shares. If no Class is specified, the Transfer Agent will
not process the transaction until the proper Class is identified. The minimum
initial purchase in the case of investments through EasyInvest(SM), an automatic
purchase plan (see "Shareholder Services"), is $100, provided that the schedule
of automatic investments will result in investments totalling at least $1,000
within the first twelve months. The minimum initial purchase in the case of an
"Education IRA" is $500, if the Distributor has reason to believe that
additional investments will increase the investment in the account to $1,000
within three years. In the case of investments pursuant to (i) Systematic
Payroll Deduction Plans (including Individual Retirement Plans), (ii) the MSDW
Advisors mutual fund asset allocation program and (iii) fee-based programs
approved by the Distributor,


                                                                             15
<PAGE>

pursuant to which participants pay an asset based fee for services in the
nature of investment advisory, administrative and/or brokerage services, the
Fund, in its discretion, may accept investments without regard to any minimum
amounts which would otherwise be required, provided, in the case of Systematic
Payroll Deduction Plans, that the Distributor has reason to believe that
additional investments will increase the investment in all accounts under such
Plans to at least $1,000. Certificates for shares purchased will not be issued
unless a request is made by the shareholder in writing to the Transfer Agent.

      Shares of the Fund are sold through the Distributor on a normal three
business day settlement basis; that is, payment is due on the third business
day (settlement date) after the order is placed with the Distributor. Since DWR
and other Selected Broker-Dealers forward investors' funds on settlement date,
they will benefit from the temporary use of the funds if payment is made prior
thereto. As noted above, orders placed directly with the Transfer Agent must be
accompanied by payment. Investors will be entitled to receive income dividends
and capital gains distributions if their order is received by the close of
business on the day prior to the record date for such dividends and
distributions. Sales personnel of a Selected Broker-Dealer are compensated for
selling shares of the Fund by the Distributor and/or the Selected Broker-Dealer
or any of its affiliates. In addition, some sales personnel of the Selected
Broker-Dealer will receive non-cash compensation as special sales incentives,
including trips, educational and/or business seminars and merchandise. The Fund
and the Distributor reserve the right to reject any purchase orders.



ALTERNATIVE PURCHASE ARRANGEMENTS

The Fund offers several Classes of shares to investors designed to provide them
with the flexibility of selecting an investment best suited to their needs. The
general public is offered three Classes of shares: Class A shares, Class B
shares and Class C shares, which differ principally in terms of sales charges
and rate of expenses to which they are subject. A fourth Class of shares, Class
D shares, is offered only to limited categories of investors (see "No Load
Alternative--Class D Shares" below).

      Each Class A, Class B, Class C or Class D share of the Fund represents an
identical interest in the investment portfolio of the Fund except that Class A,
Class B and Class C shares bear the expenses of the ongoing shareholder service
fees, Class B and Class C shares bear the expenses of the ongoing distribution
fees and Class A, Class B and Class C shares which are redeemed subject to a
CDSC bear the expense of the additional incremental distribution costs
resulting from the CDSC applicable to shares of those Classes. The ongoing
distribution fees that are imposed on Class A, Class B and Class C shares will
be imposed directly against those Classes and not against all assets of the
Fund and, accordingly, such charges against one Class will not affect the net
asset value of any other Class or have any impact on investors choosing another
sales charge option. See "Plan of Distribution" and "Redemptions and
Repurchases."

      Set forth below is a summary of the differences between the Classes and
the factors an investor should consider when selecting a particular Class. This
summary is qualified in its entirety by detailed discussion of each Class that
follows this summary.

CLASS A SHARES. Class A shares are sold at net asset value plus an initial
sales charge of up to 5.25%. The initial sales charge is reduced for certain
purchases. Investments of $1 million or more (and investments by certain other
limited categories of investors) are not subject to any sales charges at the
time of purchase but are subject to a CDSC of 1.0% on redemptions made within
one year after purchase, except for certain specific circumstances. Class A
shares are also subject to a 12b-1 fee of up to 0.25% of the average daily net
assets of the Class. See "Initial Sales Charge Alternative--Class A Shares."

CLASS B SHARES. Class B shares are offered at net asset value with no initial
sales charge but are subject to a CDSC (scaled down from 5.0% to 1.0%) if
redeemed within six years of purchase. (Class B shares purchased by certain
qualified plans are subject to a CDSC scaled down from 2.0% to 1.0% if redeemed
within three years after purchase.) This CDSC may be waived for certain
redemptions. Class B shares are also subject to an annual 12b-1 fee of 1.0% of
the lesser of: (a) the average daily aggregate gross sales of the Fund's Class
B shares since the inception of the Fund (not including reinvestments of
dividends or capital gains distributions), less the average daily aggregate net
asset value of the Fund's Class B shares redeemed since the Fund's inception
upon which a CDSC has been imposed or waived, or (b) the average daily net
assets of Class B. The Class B shares' distribution fee will cause that Class
to have higher expenses and pay lower dividends than Class A or Class D shares.
 

      After approximately ten (10) years, Class B shares will convert
automatically to Class A shares of the Fund, based on the relative net asset
values of the shares of the two Classes on the conversion date. In addition, a
certain portion of Class B shares that have been acquired through the
reinvestment of dividends and distributions


16
<PAGE>

will be converted at that time. See "Contingent Deferred Sales Charge
Alternative--Class B Shares."

CLASS C SHARES. Class C shares are sold at net asset value with no initial
sales charge but are subject to a CDSC of 1.0% on redemptions made within one
year after purchase. This CDSC may be waived for certain redemptions. They are
subject to an annual 12b-1 fee of up to 1.0% of the average daily net assets of
the Class C shares. The Class C shares' distribution fee may cause that Class
to have higher expenses and pay lower dividends than Class A or Class D shares.
See "Level Load Alternative--Class C Shares."

CLASS D SHARES. Class D shares are available only to limited categories of
investors (see "No Load Alternative--Class D Shares" below). Class D shares are
sold at net asset value with no initial sales charge or CDSC. They are not
subject to any 12b-1 fees. See "No Load Alternative--Class D Shares."

SELECTING A PARTICULAR CLASS. In deciding which Class of Fund shares to
purchase, investors should consider the following factors, as well as any other
relevant facts and circumstances:

      The decision as to which Class of shares is more beneficial to an
investor depends on the amount and intended length of his or her investment.
Investors who prefer an initial sales charge alternative may elect to purchase
Class A shares. Investors qualifying for significantly reduced or, in the case
of purchases of $1 million or more, no initial sales charges may find Class A
shares particularly attractive because similar sales charge reductions are not
available with respect to Class B or Class C shares. Moreover, Class A shares
are subject to lower ongoing expenses than are Class B or Class C shares over
the term of the investment. As an alternative, Class B and Class C shares are
sold without any initial sales charge so the entire purchase price is
immediately invested in the Fund. Any investment return on these additional
investment amounts may partially or wholly offset the higher annual expenses of
these Classes. Because the Fund's future return cannot be predicted, however,
there can be no assurance that this would be the case.

      Finally, investors should consider the effect of the CDSC period and any
conversion rights of the Classes in the context of their own investment time
frame. For example, although Class C shares are subject to a significantly
lower CDSC upon redemptions, they do not, unlike Class B shares, convert into
Class A shares after approximately ten years, and, therefore, are subject to an
ongoing 12b-1 fee of 1.0% (rather than the 0.25% fee applicable to Class A
shares) for an indefinite period of time. Thus, Class B shares may be more
attractive than Class C shares to investors with longer term investment
outlooks. Other investors, however, may elect to purchase Class C shares if,
for example, they determine that they do not wish to be subject to a front-end
sales charge and they are uncertain as to the length of time they intend to
hold their shares.

      For the purpose of meeting the $5 million (or $25 million) minimum
investment amount for Class D shares, holdings of Class A shares in all Morgan
Stanley Dean Witter Multi-Class Funds, shares of FSC Funds and shares of Morgan
Stanley Dean Witter Funds for which such shares have been exchanged will be
included together with the current investment amount.

      Sales personnel may receive different compensation for selling each Class
of shares. Investors should understand that the purpose of a CDSC is the same
as that of the initial sales charge in that the sales charges applicable to
each Class provide for the financing of the distribution of shares of that
Class.

      Set forth below is a chart comparing the sales charge, 12b-1 fees and
conversion options applicable to each Class of shares:


                                                         Conversion
 Class          Sales Charge          12b-1 Fee           Feature
- -------   ------------------------   -----------   ---------------------

    A     Maximum 5.25%                0.25%                  No
          initial sales charge
          reduced for purchases
          of $25,000 and over;
          shares sold without
          an initial sales charge
          generally subject to
          a 1.0% CDSC during
          first year.
    B     Maximum 5.0%                  1.0%            B shares convert
          CDSC during the first                         to A shares
          year decreasing                               automatically
          to 0 after six years                          after approximately
                                                        ten years
    C     1.0% CDSC during              1.0%                  No
          first year
    D               None                None                  No


      See "Purchase of Fund Shares" and "The Fund and its Management" for a
complete description of the sales charges and service and distribution fees for
each Class of shares and "Determination of Net Asset Value," "Dividends,
Distributions and Taxes" and "Shareholder Services--Exchange Privilege" for
other differences between the Classes of shares.
<PAGE>
INITIAL SALES CHARGE ALTERNATIVE--
CLASS A SHARES

Class A shares are sold at net asset value plus an initial sales charge. In
some cases, reduced sales charges may be available, as described below.
Investments of $1 million or more (and investments by certain other limited


                                                                             17
<PAGE>

categories of investors) are not subject to any sales charges at the time of
purchase but are subject to a CDSC of 1.0% on redemptions made within one year
after purchase (calculated from the last day of the month in which the shares
were purchased), except for certain specific circumstances. The CDSC will be
assessed on an amount equal to the lesser of the current market value or the
cost of the shares being redeemed. The CDSC will not be imposed (i) in the
circumstances set forth below in the section "Contingent Deferred Sales Charge
Alternative--Class B Shares--CDSC Waivers," except that the references to six
years in the first paragraph of that section shall mean one year in the case of
Class A shares, and (ii) in the circumstances identified in the section
"Additional Net Asset Value Purchase Options" below. Class A shares are also
subject to an annual 12b-1 fee of up to 0.25% of the average daily net assets
of the Class.

      The offering price of Class A shares will be the net asset value per
share next determined following receipt of an order (see "Determination of Net
Asset Value" below), plus a sales charge (expressed as a percentage of the
offering price) on a single transaction as shown in the following table:



<TABLE>
<CAPTION>
                                            Sales Charge
                                ------------------------------------
                                  Percentage of        Approximate
       Amount of Single          Public Offering      Percentage of
         Transaction                  Price          Amount Invested
- -----------------------------   -----------------   ----------------
<S>                             <C>                        <C>
Less than $25,000 ...........   5.25%                      5.54%
$25,000 but less
   than $50,000 .............   4.75%                      4.99%
$50,000 but less
   than $100,000 ............   4.00%                      4.17%
$100,000 but less
   than $250,000 ............   3.00%                      3.09%
$250,000 but less
   than $1 million ..........   2.00%                      2.04%
$1 million and over .........      0                          0
</TABLE>
      Upon notice to all Selected Broker-Dealers, the Distributor may reallow
up to the full applicable sales charge as shown in the above schedule during
periods specified in such notice. During periods when 90% or more of the sales
charge is reallowed, such Selected Broker-Dealers may be deemed to be
underwriters as that term is defined in the Securities Act of 1933.

      The above schedule of sales charges is applicable to purchases in a
single transaction by, among others: (a) an individual; (b) an individual, his
or her spouse and their children under the age of 21 purchasing shares for his,
her or their own accounts; (c) a trustee or other fiduciary purchasing shares
for a single trust estate or a single fiduciary account; (d) a pension,
profit-sharing or other employee benefit plan qualified or non-qualified under
Section 401 of the Internal Revenue Code; (e) tax-exempt organizations
enumerated in Section 501(c)(3) or (13) of the Internal Revenue Code; (f)
employee benefit plans qualified under Section 401 of the Internal Revenue Code
of a single employer or of employers who are "affiliated persons" of each other
within the meaning of Section 2(a)(3)(c) of the Act; and for investments in
Individual Retirement Accounts of employees of a single employer through
Systematic Payroll Deduction plans; or (g) any 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.

COMBINED PURCHASE PRIVILEGE. Investors may have the benefit of reduced sales
charges in accordance with the above schedule by combining purchases of Class A
shares of the Fund in single transactions with the purchase of Class A shares
of other Morgan Stanley Dean Witter Multi-Class Funds and shares of FSC Funds.
The sales charge payable on the purchase of the Class A shares of the Fund, the
Class A shares of the other Morgan Stanley Dean Witter Multi-Class Funds and
the shares of the FSC Funds will be at their respective rates applicable to the
total amount of the combined concurrent purchases of such shares.

RIGHT OF ACCUMULATION. The above persons and entities may benefit from a
reduction of the sales charges in accordance with the above schedule if the
cumulative net asset value of Class A shares purchased in a single transaction,
together with shares of the Fund and other Morgan Stanley Dean Witter Funds
previously purchased at a price including a front-end sales charge (including
shares of the Fund and other Morgan Stanley Dean Witter Funds acquired in
exchange for those shares, and including in each case shares acquired through
reinvestment of dividends and distributions), which are held at the time of
such transaction, amounts to $25,000 or more. If such investor has a cumulative
net asset value of shares of FSC Funds and Class A and Class D shares that,
together with the current investment amount, is equal to at least $5 million
($25 million for certain qualified plans), such investor is eligible to
purchase Class D shares subject to the $1,000 minimum initial investment
requirement of that Class of the Fund. See "No Load Alternative--Class D
Shares" below.

      The Distributor must be notified by DWR or a Selected Broker-Dealer or
the shareholder at the time a purchase order is placed that the purchase
qualifies for the reduced charge under the Right of Accumulation. Similar
notification must be made in writing by the dealer or shareholder when such an
order is placed by mail. The reduced sales charge will not be granted if: (a)
such notification is not furnished at the time of the order; or

18
<PAGE>

(b) a review of the records of the Selected Broker-Dealer or the Transfer Agent
fails to confirm the investor's represented holdings.

LETTER OF INTENT. The foregoing schedule of reduced sales charges will also be
available to investors who enter into a written Letter of Intent providing for
the purchase, within a thirteen-month period, of Class A shares of the Fund
from DWR or other Selected Broker-Dealers. The cost of Class A shares of the
Fund or shares of other Morgan Stanley Dean Witter Funds which were previously
purchased at a price including a front-end sales charge during the 90-day
period prior to the date of receipt by the Distributor of the Letter of Intent,
or of Class A shares of the Fund or shares of other Morgan Stanley Dean Witter
Funds acquired in exchange for shares of such funds purchased during such
period at a price including a front-end sales charge, which are still owned by
the shareholder, may also be included in determining the applicable reduction.

ADDITIONAL NET ASSET VALUE PURCHASE OPTIONS. In addition to investments of $1
million or more, Class A shares also may be purchased at net asset value by the
following:

      (1) trusts for which MSDW Trust (which is an affiliate of the Investment
Manager) provides discretionary trustee services;

      (2) persons participating in a fee-based program approved by the
Distributor, pursuant to which such persons pay an asset based fee for services
in the nature of investment advisory, administrative and/or brokerage services
(such investments are subject to all of the terms and conditions of such
programs, which may include termination fees, mandatory redemption upon
termination and such other circumstances specified in the programs' agreements
and restrictions on transferability of Fund shares);

      (3) employer-sponsored 401(k) and other plans qualified under Section
401(a) of the Internal Revenue Code ("Qualified Retirement Plans") with at
least 200 eligible employees and for which MSDW Trust serves as Trustee or
DWR's Retirement Plan Services serves as recordkeeper pursuant to a written
Recordkeeping Services Agreement;

      (4) Qualified Retirement Plans for which MSDW Trust serves as Trustee or
DWR's Retirement Plan Services serves as recordkeeper pursuant to a written
Recordkeeping Services Agreement whose Class B shares have converted to Class A
shares, regardless of the plan's asset size or number of eligible employees;

      (5) investors who are clients of a Morgan Stanley Dean Witter Financial
Advisor who joined Morgan Stanley Dean Witter from another investment firm
within six months prior to the date of purchase of Fund shares by such
investors, if the shares are being purchased with the proceeds from a
redemption of shares of an open-end proprietary mutual fund of the Financial
Advisor's previous firm which imposed either a front-end or deferred sales
charge, provided such purchase was made within sixty days after the redemption
and the proceeds of the redemption had been maintained in the interim in cash
or a money market fund; and

      (6) other categories of investors, at the discretion of the Board, as
disclosed in the then current prospectus of the Fund.

      No CDSC will be imposed on redemptions of shares purchased pursuant to
paragraphs (1), (2) or (5), above.

      For further information concerning purchases of the Fund's shares,
contact DWR or another Selected Broker-Dealer or consult the Statement of
Additional Information.




CONTINGENT DEFERRED SALES CHARGE
ALTERNATIVE--CLASS B SHARES

Class B shares are sold at net asset value next determined without an initial
sales charge so that the full amount of an investor's purchase payment may be
immediately invested in the Fund. A CDSC, however, will be imposed on most
Class B shares redeemed within six years after purchase. The CDSC will be
imposed on any redemption of shares if after such redemption the aggregate
current value of a Class B account with the Fund falls below the aggregate
amount of the investor's purchase payments for Class B shares made during the
six years (or, in the case of shares held by certain Qualified Retirement
Plans, three years) preceding the redemption. In addition, Class B shares are
subject to an annual 12b-1 fee of 1.0% of the lesser of: (a) the average daily
aggregate gross sales of the Fund's Class B shares since the inception of the
Fund (not including reinvestments of dividends or capital gains distributions),
less the average daily aggregate net asset value of the Fund's Class B shares
redeemed since the Fund's inception upon which a CDSC has been imposed or
waived, or (b) the average daily net assets of Class B.

      Except as noted below, Class B shares of the Fund which are held for six
years or more after purchase (calculated from the last day of the month in
which the shares were purchased) will not be subject to any CDSC upon
redemption. Shares redeemed earlier than six years after purchase may, however,
be subject to a CDSC which will be a percentage of the dollar amount of shares
redeemed and will be assessed on an amount equal to the lesser of the current
market value or the cost of the


                                                                             19
<PAGE>

shares being redeemed. The size of this percentage will depend upon how long
the shares have been held, as set forth in the following table:



<TABLE>
<CAPTION>
           Year Since
            Purchase                CDSC as a Percentage
          Payment Made               of Amount Redeemed
- --------------------------------   ---------------------
<S>                                          <C>
First ..........................            5.0%
Second .........................            4.0%
Third ..........................            3.0%
Fourth .........................            2.0%
Fifth ..........................            2.0%
Sixth ..........................            1.0%
Seventh and thereafter .........            None
</TABLE>

      In the case of Class B shares of the Fund purchased on or after July 28,
1997 by Qualified Retirement Plans for which MSDW Trust serves as Trustee or
DWR's Retirement Plan Services serves as recordkeeper pursuant to a written
Recordkeeping Services Agreement, shares held for three years or more after
purchase (calculated as described in the paragraph above) will not be subject
to any CDSC upon redemption. However, shares redeemed earlier than three years
after purchase may be subject to a CDSC (calculated as described in the
paragraph above), the percentage of which will depend on how long the shares
have been held, as set forth in the following table:



<TABLE>
<CAPTION>
           Year Since
            Purchase               CDSC as a Percentage
          Payment Made              of Amount Redeemed
- -------------------------------   ---------------------
<S>                                          <C>
First .........................             2.0%
Second ........................             2.0%
Third .........................             1.0%
Fourth and thereafter .........             None
</TABLE>

CDSC WAIVERS. A CDSC will not be imposed on: (i) any amount which represents an
increase in value of shares purchased within the six years (or, in the case of
shares held by certain Qualified Retirement Plans, three years) preceding the
redemption; (ii) the current net asset value of shares purchased more than six
years (or, in the case of shares held by certain Qualified Retirement Plans,
three years) prior to the redemption; and (iii) the current net asset value of
shares purchased through reinvestment of dividends or distributions and/or
shares acquired in exchange for shares of FSC Funds or of other Morgan Stanley
Dean Witter Funds acquired in exchange for such shares. Moreover, in
determining whether a CDSC is applicable it will be assumed that amounts
described in (i), (ii) and (iii) above (in that order) are redeemed first.

      In addition, the CDSC, if otherwise applicable, will be waived in the
case of:

      (1) redemptions of shares held at the time a shareholder dies or becomes
disabled, only if the shares are:

      (a) registered either in the name of an individual shareholder (not a
trust), or in the names of such shareholder and his or her spouse as joint
tenants with right of survivorship; or   (b) held in a qualified corporate or
self-employed retirement plan, Individual Retirement Account ("IRA") or
Custodial Account under Section 403(b)(7) of the Internal Revenue Code ("403(b)
Custodial Account"), provided in either case that the redemption is requested
within one year of the death or initial determination of disability;

      (2) redemptions in connection with the following retirement plan
distributions:   (a) lump-sum or other distributions from a qualified corporate
or self-employed retirement plan following retirement (or, in the case of a
"key employee" of a "top heavy" plan, following attainment of age 59 1/2);
  (b) distributions from an IRA or 403(b) Custodial Account following
attainment of age 59 1/2; or   (c) a tax-free return of an excess contribution
to an IRA;

      (3) all redemptions of shares held for the benefit of a participant in a
Qualified Retirement Plan which offers investment companies managed by the
Investment Manager or its subsidiary, MSDW Services, as self-directed
investment alternatives and for which MSDW Trust serves as Trustee or DWR's
Retirement Plan Services serves as recordkeeper pursuant to a written
Recordkeeping Services Agreement ("Eligible Plan"), provided that either:   (a)
the plan continues to be an Eligible Plan after the redemption; or   (b) the
redemption is in connection with the complete termination of the plan involving
the distribution of all plan assets to participants; and

      (4) certain redemptions pursuant to the Fund's Systematic Withdrawal Plan
(see "Shareholder Services--Systematic Withdrawal Plan").

      With reference to (1) above, for the purpose of determining disability,
the Distributor utilizes the definition of disability contained in Section
72(m)(7) of the Internal Revenue Code, which relates to the inability to engage
in gainful employment. With reference to (2) above, the term "distribution"
does not encompass a direct transfer of IRA, 403(b) Custodial Account or
retirement plan assets to a successor custodian or trustee. All waivers will be
granted only following receipt by the Distributor of confirmation of the
shareholder's entitlement.

CONVERSION TO CLASS A SHARES. All shares of the Fund held prior to July 28,
1997 have been designated Class B shares. Shares held before May 1, 1997 will
convert to Class A shares in May, 2007. In all other instances Class B shares
will convert automatically to Class A shares, based on the relative net asset
values of the shares of the


20
<PAGE>

two Classes on the conversion date, which will be approximately ten (10) years
after the date of the original purchase. The ten year period is calculated from
the last day of the month in which the shares were purchased or, in the case of
Class B shares acquired through an exchange or a series of exchanges, from the
last day of the month in which the original Class B shares were purchased,
provided that shares originally purchased before May 1, 1997 will convert to
Class A shares in May, 2007. The conversion of shares purchased on or after May
1, 1997 will take place in the month following the tenth anniversary of the
purchase. There will also be converted at that time such proportion of Class B
shares acquired through automatic reinvestment of dividends and distributions
owned by the shareholder as the total number of his or her Class B shares
converting at the time bears to the total number of outstanding Class B shares
purchased and owned by the shareholder. In the case of Class B shares held by a
Qualified Retirement Plan for which MSDW Trust serves as Trustee or DWR's
Retirement Plan Services serves as recordkeeper pursuant to a written
Recordkeeping Services Agreement, the plan is treated as a single investor and
all Class B shares will convert to Class A shares on the conversion date of the
first shares of a Morgan Stanley Dean Witter Multi-Class Fund purchased by that
plan. In the case of Class B shares previously exchanged for shares of an
"Exchange Fund" (see "Shareholder Services--Exchange Privilege"), the period of
time the shares were held in the Exchange Fund (calculated from the last day of
the month in which the Exchange Fund shares were acquired) is excluded from the
holding period for conversion. If those shares are subsequently re-exchanged
for Class B shares of a Morgan Stanley Dean Witter Multi-Class Fund, the
holding period resumes on the last day of the month in which Class B shares are
reacquired.

      If a shareholder has received share certificates for Class B shares, such
certificates must be delivered to the Transfer Agent at least one week prior to
the date for conversion. Class B shares evidenced by share certificates that
are not received by the Transfer Agent at least one week prior to any
conversion date will be converted into Class A shares on the next scheduled
conversion date after such certificates are received.

      Effectiveness of the conversion feature is subject to the continuing
availability of a ruling of the Internal Revenue Service or an opinion of
counsel that (i) the conversion of shares does not constitute a taxable event
under the Internal Revenue Code, (ii) Class A shares received on conversion
will have a basis equal to the shareholder's basis in the converted Class B
shares immediately prior to the conversion, and (iii) Class A shares received
on conversion will have a holding period that includes the holding period of
the converted Class B shares. The conversion feature may be suspended if the
ruling or opinion is no longer available. In such event, Class B shares would
continue to be subject to Class B 12b-1 fees.




LEVEL LOAD ALTERNATIVE--CLASS C SHARES

Class C shares are sold at net asset value next determined without an initial
sales charge but are subject to a CDSC of 1.0% on most redemptions made within
one year after purchase (calculated from the last day of the month in which the
shares were purchased). The CDSC will be assessed on an amount equal to the
lesser of the current market value or the cost of the shares being redeemed.
The CDSC will not be imposed in the circumstances set forth above in the
section "Contingent Deferred Sales Charge Alternative--Class B Shares--CDSC
Waivers," except that the references to six years in the first paragraph of
that section shall mean one year in the case of Class C shares. Class C shares
are subject to an annual 12b-1 fee of up to 1.0% of the average daily net
assets of the Class. Unlike Class B shares, Class C shares have no conversion
feature and, accordingly, an investor that purchases Class C shares will be
subject to 12b-1 fees applicable to Class C shares for an indefinite period
subject to annual approval by the Fund's Board of Trustees and regulatory
limitations.




NO LOAD ALTERNATIVE--CLASS D SHARES

Class D shares are offered without any sales charge on purchase or redemption
and without any 12b-1 fee. Class D shares are offered only to investors meeting
an initial investment minimum of $5 million ($25 million for Qualified
Retirement Plans for which MSDW Trust serves as Trustee or DWR's Retirement
Plan Services serves as recordkeeper pursuant to a written Recordkeeping
Services Agreement) and the following categories of investors: (i) investors
participating in the MSDW Advisors mutual fund asset allocation program
pursuant to which such persons pay an asset based fee; (ii) persons
participating in a fee-based program approved by the Distributor, pursuant to
which such persons pay an asset based fee for services in the nature of
investment advisory, administrative and/or brokerage services (subject to all
of the terms and conditions of such programs referred to in (i) or (ii) above
which may include termination fees mandatory redemption upon termination and
restrictions on transferability of Fund shares); (iii) 401(k) plans established
by DWR and SPS Transaction Services, Inc. (an affiliate of DWR) for their
employees; (iv) certain Unit Investment Trusts sponsored by DWR; (v) certain


                                                                             21
<PAGE>

other open-end investment companies whose shares are distributed by the
Distributor; (vi) investors who were shareholders of Dean Witter Retirement
Series on September 11, 1998 (with respect to additional purchases for their
former Dean Witter Retirement Series accounts); and (vii) other categories of
investors, at the discretion of the Board, as disclosed in the then current
prospectus of the Fund. Investors who require a $5 million (or $25 million)
minimum initial investment to qualify to purchase Class D shares may satisfy
that requirement by investing that amount in a single transaction in Class D
shares of the Fund and other Morgan Stanley Dean Witter Multi-Class Funds,
subject to the $1,000 minimum initial investment required for that Class of the
Fund. In addition, for the purpose of meeting the $5 million minimum investment
amount, holdings of Class A shares in all Morgan Stanley Dean Witter
Multi-Class Funds, shares of FSC Funds and shares of Morgan Stanley Dean Witter
Funds for which such shares have been exchanged will be included together with
the current investment amount. If a shareholder redeems Class A shares and
purchases Class D shares, such redemption may be a taxable event.



PLAN OF DISTRIBUTION

The Fund has adopted a Plan of Distribution pursuant to Rule 12b-1 under the
Act with respect to the distribution of Class A, Class B and Class C shares of
the Fund. In the case of Class A and Class C shares, the Plan provides that the
Fund will reimburse the Distributor and others for the expenses of certain
activities and services incurred by them specifically on behalf of those
shares. Reimbursements for these expenses will be made in monthly payments by
the Fund to the Distributor, which will in no event exceed amounts equal to
payments at the annual rates of 0.25% and 1.0% of the average daily net assets
of Class A and Class C, respectively. In the case of Class B shares, the Plan
provides that the Fund will pay the Distributor a fee, which is accrued daily
and paid monthly, at the annual rate of 1.0% of the lesser of: (a) the average
daily aggregate gross sales of the Fund's Class B shares since the inception of
the Fund (not including reinvestments of dividends or capital gains
distributions), less the average daily aggregate net asset value of the Fund's
Class B shares redeemed since the Fund's inception upon which a CDSC has been
imposed or waived, or (b) the average daily net assets of Class B. The fee is
treated by the Fund as an expense in the year it is accrued. In the case of
Class A shares, the entire amount of the fee currently represents a service fee
within the meaning of the NASD guidelines. In the case of Class B and Class C
shares, a portion of the fee payable pursuant to the Plan, equal to 0.25% of
the average daily net assets of each of these Classes, is currently
characterized as a service fee. A service fee is a payment made for personal
service and/or the maintenance of shareholder accounts.

      Additional amounts paid under the Plan in the case of Class B and Class C
shares are paid to the Distributor for services provided and the expenses borne
by the Distributor and others in the distribution of the shares of those
Classes, including the payment of commissions for sales of the shares of those
Classes and incentive compensation to and expenses of Morgan Stanley Dean
Witter Financial Advisors and others who engage in or support distribution of
shares or who service shareholder accounts, including overhead and telephone
expenses; printing and distribution of prospectuses and reports used in
connection with the offering of the Fund's shares to other than current
shareholders; and preparation, printing and distribution of sales literature
and advertising materials. In addition, the Distributor may utilize fees paid
pursuant to the Plan in the case of Class B shares to compensate DWR and other
Selected Broker-Dealers for their opportunity costs in advancing such amounts,
which compensation would be in the form of a carrying charge on any
unreimbursed expenses.

      For the fiscal year ended July 31, 1998, Class B shares of the Fund
accrued payments under the Plan amounting to $4,014,573, which amount is equal
to 1.0% of the average daily net assets of Class B for the fiscal year. These
payments were calculated pursuant to clause (b) of the compensation formula
under the Plan. For the fiscal year ended July 31, 1998, Class A and Class C
shares of the Fund accrued payments under the Plan amounting to $345 and
$2,652, respectively, which amounts are equal to 0.24% and 1.0% of the average
daily net assets of Class A and Class C, respectively, for the fiscal year.

      In the case of Class B shares, at any given time, the expenses in
distributing Class B shares of the Fund may be in excess of the total of (i)
the payments made by the Fund pursuant to the Plan, and (ii) the proceeds of
CDSCs paid by investors upon the redemption of Class B shares. For example, if
$1 million in expenses in distributing Class B shares of the Fund had been
incurred and $750,000 had been received as described in (i) and (ii) above, the
excess expense would amount to $250,000. The Distributor has advised the Fund
that such excess amounts, including the carrying charge described above,
totalled $13,965,055 at July 31, 1998, which was equal to 3.93% of the net
assets of Class B on such date. Because there is no requirement under the Plan
that the Distributor be reimbursed for all distribution expenses or any
requirement that the Plan be continued from year to year, such excess amount
does not constitute a liability of the Fund. Although there is no legal
obligation for the Fund


22
<PAGE>

to pay expenses incurred in excess of payments made to the Distributor under
the Plan, and the proceeds of CDSCs paid by investors upon redemption of
shares, if for any reason the Plan is terminated the Trustees will consider at
that time the manner in which to treat such expenses. Any cumulative expenses
incurred, but not yet recovered through distribution fees or CDSCs, may or may
not be recovered through future distribution fees or CDSCs.

      In the case of Class A and Class C shares, expenses incurred pursuant to
the Plan in any calendar year in excess of 0.25% or 1.0% of the average daily
net assets of Class A or Class C, respectively, will not be reimbursed by the
Fund through payments in any subsequent year, except that expenses representing
a gross sales commission credited to Morgan Stanley Dean Witter Financial
Advisors and other Selected Broker-Dealer representatives at the time of sale
may be reimbursed in the subsequent calendar year. The Distributor has advised
the Fund that unreimbursed expenses representing a gross sales commissions
credited to Morgan Stanley Dean Witter Financial Advisors and other Selected
Broker-Dealer representatives at the time of sale totalled $1,248 in the case
of Class C at December 31, 1997, which was equal to 0.70% of the net assets of
Class C on such date, and that there were no such expenses which may be
reimbursed in the subsequent year in the case of Class A on such date. No
interest or other financing charges will be incurred on any Class A or Class C
distribution expenses incurred by the Distributor under the Plan or on any
unreimbursed expenses due to the Distributor pursuant to the Plan.



DETERMINATION OF NET ASSET VALUE

The net asset value per share is determined once daily at 4:00 p.m., New York
time (or, on days when the New York Stock Exchange closes prior to 4:00 p.m.,
at such earlier time), on each day that the New York Stock Exchange is open by
taking the net assets of the Fund, dividing by the number of shares outstanding
and adjusting to the nearest cent. The assets belonging to the Class A, Class
B, Class C and Class D shares will be invested together in a single portfolio.
The net asset value of each Class, however, will be determined separately by
subtracting each Class's accrued expenses and liabilities. The net asset value
per share will not be determined on Good Friday and on such other federal and
non-federal holidays as are observed by the New York Stock Exchange.

      In the calculation of the Fund's net asset value: (1) an equity portfolio
security listed or traded on the New York or American Stock Exchange or other
domestic or foreign stock exchange is valued at its latest sale price on that
exchange prior to the time when assets are valued; if there were no sales that
day, the security is valued at the latest bid price (in cases where securities
are traded on more than one exchange, the securities are valued on the exchange
designated as the primary market pursuant to procedures adopted by the
Trustees); and (2) all other portfolio securities for which over-the-counter
market quotations are readily available are valued at the latest available bid
price prior to the time of valuation. When market quotations are not readily
available, including circumstances under which it is determined by the
Investment Manager that sale or bid prices are not reflective of a security's
market value, portfolio securities are valued at their fair value as determined
in good faith under procedures established by and under the general supervision
of the Fund's Trustees. For valuation purposes, quotations of foreign portfolio
securities, other assets and liabilities and forward contracts stated in
foreign currency are translated into U.S. dollar equivalents at the prevailing
market rates as of the morning of valuation. Dividends receivable are accrued
as of the ex-dividend date or as of the time that the relevant ex-dividend date
and amounts become known.

      Certain of the Fund's portfolio securities may be valued by an outside
pricing service approved by the Fund's Trustees. The pricing service may
utilize a matrix system incorporating security quality, maturity and coupon as
the evaluation model parameters, and/or research evaluations by its staff,
including review of broker-dealer market price quotations, in determining what
it believes is the fair valuation of the portfolio securities valued by such
pricing service.

SHAREHOLDER SERVICES
- -------------------------------------------------------------------------------

AUTOMATIC INVESTMENT OF DIVIDENDS AND DISTRIBUTIONS. All income dividends and
capital gains distributions are automatically paid in full and fractional
shares of the applicable Class of the Fund, (or, if specified by the
shareholder, in shares of any other open-end Morgan Stanley Dean Witter Fund),
unless the shareholder requests that they be paid in cash. Shares so acquired
are acquired at net asset value and are not subject to the imposition of a
front-end sales charge or a CDSC (see "Redemptions and Repurchases").


INVESTMENT OF DIVIDENDS OR DISTRIBUTIONS RECEIVED IN CASH. Any shareholder who
receives a cash payment representing a dividend or capital gains distribution
may invest


                                                                             23
<PAGE>

such dividend or distribution in shares of the applicable Class at the net
asset value next determined after receipt by the Transfer Agent by returning
the check or the proceeds to the Transfer Agent within 30 days after the
payment date. Shares so acquired are acquired at net asset value and are not
subject to the imposition of a front-end sales charge or a CDSC (see
"Redemptions and Repurchases").

EASYINVEST(SM). Shareholders may subscribe to EasyInvest, an automatic purchase
plan which provides for any amount from $100 to $5,000 to betransferred
automatically from a checking or savings account or following redemption of
shares of a Morgan Stanley Dean Witter money market fund, on a semi-monthly,
monthly or quarterly basis, to the Fund's Transfer Agent for investment in
shares of the Fund (see "Purchase of Fund Shares" and "Redemptions and
Repurchases--Involuntary Redemption").

SYSTEMATIC WITHDRAWAL PLAN. A systematic withdrawal plan (the "Withdrawal
Plan") is available for shareholders whose shares of Morgan Stanley Dean Witter
Funds have an aggregate value of $10,000 or more. Shares of any Fund from which
redemptions will be made pursuant to the Plan must have a value of $1,000 or
more (referred to as a "SWP Fund"). The required share values are determined on
the date the shareholder establishes the Withdrawal Plan. The Withdrawal Plan
provides for monthly, quarterly, semi-annual or annual payments in any amount
not less than $25, or in any whole percentage of the value of the SWP Funds'
shares, on an annualized basis. Any applicable CDSC will be imposed on shares
redeemed under the Withdrawal Plan (see "Purchase of Fund Shares"), except that
the CDSC, if any, will be waived on redemptions under the Withdrawal Plan of up
to 12% annually of the value of each SWP Fund account, based on the share
values next determined after the shareholder establishes the Withdrawal Plan.
(For shareholders who established the Withdrawal Plan prior to October 1, 1998,
the value of each SWP Fund account for the purpose of the 12% CDSC waiver will
be determined at 4:00 p.m., New York time, on October 2, 1998.) Redemptions for
which this CDSC waiver policy applies may be in amounts up to 1% per month, 3%
per quarter, 6% semi-annually or 12% annually. Under this CDSC waiver policy,
amounts withdrawn each period will be paid by first redeeming shares not
subject to a CDSC because the shares were purchased by the reinvestment of
dividends or capital gains distributions, the CDSC period has elapsed or some
other waiver of the CDSC applies. If shares subject to a CDSC must be redeemed,
shares held for the longest period of time will be redeemed first and
continuing with shares held the next longest period of time until shares held
the shortest period of time are redeemed. Any shareholder participating in the
Withdrawal Plan will have sufficient shares redeemed from his or her account so
that the proceeds (net of any applicable CDSC) to the shareholder will be the
designated monthly, quarterly, semi-annual or annual amount.

      A shareholder may suspend or terminate participation in the Withdrawal
Plan at any time. A shareholder who has suspended participation may resume
payments under the Withdrawal Plan, without requiring a new determination of
the account value for the 12% CDSC waiver. The Withdrawal Plan may be
terminated or revised at any time by the Fund.

      Prior to adding an additional SWP Fund to an existing Withdrawal Plan,
the required $10,000/$1,000 share values must be met, to be calculated on the
date the shareholder adds the additional SWP Fund. However, the addition of a
new SWP Fund will not change the account value for the 12% CDSC waiver for the
SWP Funds already participating in the Withdrawal Plan.

      Withdrawal Plan payments should not be considered dividends, yields or
income. If periodic Withdrawal Plan payments continuously exceed net investment
income and net capital gains, the shareholder's original investment will be
correspondingly reduced and ultimately exhausted. Each withdrawal constitutes a
redemption of shares and any gain or loss realized must be recognized for
federal income tax purposes.

      Shareholders should contact their Morgan Stanley Dean Witter Financial
Advisor or other Selected Broker-Dealer representative or the Transfer Agent
for further information about any of the above services.

TAX SHELTERED RETIREMENT PLANS. Retirement plans are available for use by
corporations, the self-employed, Individual Retirement Accounts and Custodial
Accounts under Section 403(b)(7) of the Internal Revenue Code. Adoption of such
plans should be on advice of legal counsel or tax advisor.

      For further information regarding plan administration, custodial fees and
other details, investors should contact their Morgan Stanley Dean Witter
Financial Advisor or other Selected Broker-Dealer representative or the
Transfer Agent.

EXCHANGE PRIVILEGE. Shares of each Class may be exchanged for shares of the
same Class of any other Morgan Stanley Dean Witter Multi-Class Fund without the
imposition of any exchange fee. Shares may also be exchanged for shares of the
following funds: Morgan Stanley Dean Witter Short-Term U.S. Treasury Trust,
Morgan Stanley Dean Witter Limited Term Municipal Trust, Morgan Stanley Dean
Witter Short-Term Bond Fund and five Morgan Stanley Dean Witter Funds which


24
<PAGE>

are money market funds (the "Exchange Funds"). Class A shares may also be
exchanged for shares of Morgan Stanley Dean Witter Multi-State Municipal Series
Trust and Morgan Stanley Dean Witter Hawaii Municipal Trust, which are Morgan
Stanley Dean Witter Funds sold with a front-end sales charge ("FSC Funds").
Class B shares may also be exchanged for shares of Morgan Stanley Dean Witter
Global Short-Term Income Fund Inc. ("Global Short-Term"), which is a Morgan
Stanley Dean Witter Fund offered with a CDSC. Exchanges may be made after the
shares of the Fund acquired by purchase (not by exchange or dividend
reinvestment) have been held for thirty days. There is no waiting period for
exchanges of shares acquired by exchange or dividend reinvestment.

      An exchange to another Morgan Stanley Dean Witter Multi-Class Fund, any
FSC Fund, Global Short-Term or any Exchange Fund that is not a money market
fund is on the basis of the next calculated net asset value per share of each
fund after the exchange order is received. When exchanging into a money market
fund from the Fund, shares of the Fund are redeemed out of the Fund at their
next calculated net asset value and the proceeds of the redemption are used to
purchase shares of the money market fund at their net asset value determined
the following business day. Subsequent exchanges between any of the money
market funds and any of the Morgan Stanley Dean Witter Multi-Class Funds, FSC
Funds, Global Short-Term or any Exchange Fund that is not a money market fund
can be effected on the same basis.

      No CDSC is imposed at the time of any exchange of shares, although any
applicable CDSC will be imposed upon ultimate redemption. During the period of
time the shareholder remains in an Exchange Fund (calculated from the last day
of the month in which the Exchange Fund shares were acquired), the holding
period (for the purpose of determining the rate of the CDSC) is frozen. If
those shares are subsequently re-exchanged for shares of a Morgan Stanley Dean
Witter Multi-Class Fund or shares of Global Short-Term, the holding period
previously frozen when the first exchange was made resumes on the last day of
the month in which shares of a Morgan Stanley Dean Witter Multi-Class Fund or
shares of Global Short-Term are reacquired. Thus, the CDSC is based upon the
time (calculated as described above) the shareholder was invested in shares of
a Morgan Stanley Dean Witter Multi-Class Fund or in shares of Global Short-Term
(see "Purchase of Fund Shares"). In the case of exchanges of Class A shares
which are subject to a CDSC, the holding period also includes the time
(calculated as described above) the shareholder was invested in shares of a FSC
Fund. In the case of shares exchanged into an Exchange Fund on or after April
23, 1990, upon a redemption of shares which results in a CDSC being imposed, a
credit (not to exceed the amount of the CDSC) will be given in an amount equal
to the Exchange Fund 12b-1 distribution fees incurred on or after that date
which are attributable to those shares. (Exchange Fund 12b-1 distribution fees
are described in the prospectuses for those funds.) Class B shares of the Fund
acquired in exchange for shares of Global Short-Term or Class B shares of
another Morgan Stanley Dean Witter Multi-Class Fund having a different CDSC
schedule than that of this Fund will be subject to the higher CDSC schedule,
even if such shares are subsequently re-exchanged for shares of the fund with
the lower CDSC schedule.

ADDITIONAL INFORMATION REGARDING EXCHANGES. Purchases and exchanges should be
made for investment purposes only. A pattern of frequent exchanges may be
deemed by the Investment Manager to be abusive and contrary to the best
interests of the Fund's other shareholders and, at the Investment Manager's
discretion, may be limited by the Fund's refusal to accept additional purchases
and/or exchanges from the investor. Although the Fund does not have any
specific definition of what constitutes a pattern of frequent exchanges, and
will consider all relevant factors in determining whether a particular
situation is abusive and contrary to the best interests of the Fund and its
other shareholders, investors should be aware that the Fund and each of the
other Morgan Stanley Dean Witter Funds may in their discretion limit or
otherwise restrict the number of times this Exchange Privilege may be exercised
by any investor. Any such restriction will be made by the Fund on a prospective
basis only, upon notice to the shareholder not later than ten days following
such shareholder's most recent exchange. Also, the Exchange Privilege may be
terminated or revised at any time by the Fund and/or any of such Morgan Stanley
Dean Witter Funds for which shares of the Fund may be exchanged, upon such
notice as may be required by applicable regulatory agencies. Shareholders
maintaining margin accounts with DWR or another Selected Broker-Dealer are
referred to their Morgan Stanley Dean Witter Financial Advisor or other
Selected Broker-Dealer representative regarding restrictions on exchange of
shares of the Fund pledged in the margin account.

      The current prospectus for each fund describes its investment
objective(s) and policies, and shareholders should obtain a copy and examine it
carefully before investing. Exchanges are subject to the minimum investment
requirement of each Class of shares and any other conditions imposed by each
fund. In the case of a shareholder holding a share certificate or certificates,
no exchanges may be made until all applicable share certificates have been
received by the Transfer Agent and


                                                                             25
<PAGE>

deposited in the shareholder's account. An exchange will be treated for federal
income tax purposes the same as a repurchase or redemption of shares, on which
the shareholder may realize a capital gain or loss. However, the ability to
deduct capital losses on an exchange may be limited in situations where there
is an exchange of shares within ninety days after the shares are purchased. The
Exchange Privilege is only available in states where an exchange may legally be
made.

      If DWR or another Selected Broker-Dealer is the current dealer of record
and its account numbers are part of the account information, shareholders may
initiate an exchange of shares of the Fund for shares of any of the Morgan
Stanley Dean Witter Funds (for which the Exchange Privilege is available)
pursuant to this Exchange Privilege by contacting their Morgan Stanley Dean
Witter Financial Advisor or other Selected Broker-Dealer representative (no
Exchange Privilege Authorization Form is required). Other shareholders (and
those shareholders who are clients of DWR or another Selected Broker-Dealer but
who wish to make exchanges directly by writing or telephoning the Transfer
Agent) must complete and forward to the Transfer Agent an Exchange Privilege
Authorization Form, copies of which may be obtained from the Transfer Agent, to
initiate an exchange. If the Authorization Form is used, exchanges may be made
in writing or by contacting the Transfer Agent at (800) 869-NEWS (toll-free).

      The Fund will employ reasonable procedures to confirm that exchange
instructions communicated over the telephone are genuine. Such procedures may
include requiring various forms of personal identification such as name,
mailing address, social security or other tax identification number and DWR or
other Selected Broker-Dealer account number (if any). Telephone instructions
may also be recorded. If such procedures are not employed, the Fund may be
liable for any losses due to unauthorized or fraudulent instructions.


      Telephone exchange instructions will be accepted if received by the
Transfer Agent between 9:00 and 4:00 p.m. New York time, on any day the New
York Stock Exchange is open. Any shareholder wishing to make an exchange who
has previously filed an Exchange Privilege Authorization Form and who is unable
to reach the Fund by telephone should contact his or her Morgan Stanley Dean
Witter Financial Advisor or other Selected Broker-Dealer representative, if
appropriate, or make a written exchange request. Shareholders are advised that
during periods of drastic economic or market changes it is possible that the
telephone exchange procedures may be difficult to implement, although this has
not been the experience of the Morgan Stanley Dean Witter Funds in the past.


      For further information regarding the Exchange Privilege, shareholders
should contact their Morgan Stanley Dean Witter Financial Advisor or other
Selected Broker-Dealer representative or the Transfer Agent.

REDEMPTIONS AND REPURCHASES
- -------------------------------------------------------------------------------

REDEMPTION. Shares of each Class of the Fund can be redeemed for cash at any
time at the net asset value per share next determined less the amount of any
applicable CDSC in the case of Class A, Class B or Class C (see "Purchase of
Fund Shares"). If shares are held in a shareholder's account without a share
certificate, a written request for redemption to the Fund's Transfer Agent at
P.O. Box 983, Jersey City, N.J. 07303 is required. If certificates are held by
the shareholder, the shares may be redeemed by surrendering the certificates
with a written request for redemption along with any additional documentation
required by the Transfer Agent.

REPURCHASE. DWR and other Selected Broker-Dealers are authorized to repurchase
shares represented by a share certificate which is delivered to any of their
offices. Shares held in a shareholder's account without a share certificate may
also be repurchased by DWR and other Selected Broker-Dealers upon the
telephonic or telegraphic request of the shareholder. The repurchase price is
the net asset value next computed (see "Purchase of Fund Shares") after such
repurchase order is received by DWR or other Selected Broker-Dealer, reduced by
any applicable CDSC.

      The CDSC, if any, will be the only fee imposed by the Fund or the
Distributor. The offer by DWR and other Selected Broker-Dealers to repurchase
shares may be suspended without notice by them at any time. In that event,
shareholders may redeem their shares through the Fund's Transfer Agent as set
forth above under "Redemption."

PAYMENT FOR SHARES REDEEMED OR REPURCHASED.  Payment for shares presented for
repurchase or redemption will be made by check within seven days after receipt
by the Transfer Agent of the certificate and/or written request in good order.
Such payment may be postponed or the right of redemption suspended under
unusual circumstances, e.g., when normal trading is not taking place on


26
<PAGE>

the New York Stock Exchange. If the shares to be redeemed have recently been
purchased by check, payment of the redemption proceeds may be delayed for the
minimum time needed to verify that the check used for investment has been
honored (not more than fifteen days from the time of receipt of the check by
the Transfer Agent). Shareholders maintaining margin accounts with DWR or
another Selected Broker-Dealer are referred to their Morgan Stanley Dean Witter
Financial Advisor or other Selected Broker-Dealer representative regarding
restrictions on redemption of shares of the Fund pledged in their margin
accounts.

REINSTATEMENT PRIVILEGE. A shareholder who has had his or her shares redeemed
or repurchased and has not previously exercised this reinstatement privilege
may, within 35 days after the date of the redemption or repurchase, reinstate
any portion or all of the proceeds of such redemption or repurchase in shares
of the Fund in the same Class from which such shares were redeemed or
repurchased, at net asset value next determined after a reinstatement request,
together with the proceeds, is received by the Transfer Agent and receive a 
pro rata credit for any CDSC paid in connection with such redemption or 
repurchase.

INVOLUNTARY REDEMPTION. The Fund reserves the right, on sixty days' notice, to
redeem at their net asset value the shares of any shareholder (other than
shares held in an Individual Retirement Account or Custodial Account under
Section 403(b)(7) of the Internal Revenue Code) whose shares, due to
redemptions by the shareholder, have a value of less than $100 or such lesser
amount as may be fixed by the Board of Trustees or, in the case of an account
opened through EasyInvest(SM), if after twelve months the shareholder has
invested less than $1,000 in the account. However, before the Fund redeems such
shares and sends the proceeds to the shareholder it will notify the shareholder
that the value of the shares is less than the applicable amount and allow the
shareholder sixty days to make an additional investment in an amount which will
increase the value of the account to at least the applicable amount before the
redemption is processed. No CDSC will be imposed on any involuntary redemption.
 

DIVIDENDS, DISTRIBUTIONS AND TAXES
- -------------------------------------------------------------------------------

DIVIDENDS AND DISTRIBUTIONS. The Fund declares dividends separately for each
Class of shares and intends to pay income dividends and to distribute net
short-term and net long-term capital gains, if any, at least once each year.
The Fund may, however, determine to retain all or part of any net long-term
capital gains in any year for reinvestment.

      All dividends and any capital gains distributions will be paid in
additional shares of the same Class and automatically credited to the
shareholder's account without issuance of a share certificate unless the
shareholder requests in writing that all dividends and/or distributions be paid
in cash. Shares acquired by dividend and distribution reinvestments will not be
subject to any front-end sales charge or CDSC. Class B shares acquired through
dividend and distribution reinvestments will become eligible for conversion to
Class A shares on a pro rata basis. Distributions paid on Class A and Class D
shares will be higher than for Class B and Class C shares because distribution
fees paid by Class B and Class C shares are higher. (See "Shareholder
Services--Automatic Investment of Dividends and Distributions.")

TAXES. Because the Fund intends to distribute all of its net investment income
and any net short-term and long-term capital gains to shareholders and to
otherwise qualify as a regulated investment company under Subchapter M of the
Internal Revenue Code, it is not expected that the Fund will be required to pay
any federal income tax on such income and capital gains.

      Gains or losses on the Fund's transactions in certain listed options and
on futures and options on futures generally are treated as 60% long-term gain
or loss and 40% short-term gain or loss. When the Fund engages in options and
futures transactions, various tax regulations applicable to the Fund may have
the effect of causing the Fund to recognize a gain or loss for tax purposes
before that gain or loss is realized, or to defer recognition of a realized
loss for tax purposes. Recognition, for tax purposes, of an unrealized loss may
result in a lesser amount of the Fund's net realized gains being available for
distribution.

      Shareholders who are required to pay taxes on their income will normally
have to pay federal income taxes, and any applicable state and local income
taxes, on the dividends and distributions they receive from the Fund. Such
dividends and distributions, to the extent that they are derived from net
investment income and net short-term capital gains, are taxable to the
shareholder as ordinary dividend income regardless of whether the shareholder
receives such distributions in additional shares or in cash. Any dividends
declared in the last quarter of any calendar year which are paid in the
following calendar year prior to February 1 will be deemed, for tax purposes,
to have been received by the shareholder in the prior year.


                                                                             27
<PAGE>

      Distributions of net long-term capital gains, if any, are taxable to
shareholders as long-term capital gains regardless of how long a shareholder
has held the Fund's shares and regardless of whether the distribution is
received in additional shares or in cash. It is anticipated that only a small
portion, if any, of the Fund's distributions may be eligible for the dividends
received deduction to corporate shareholders.

      The Fund may at times make payments from sources other than income or net
capital gains. Payments from such sources would, in effect, represent a return
of a portion of each shareholder's investment. All, or a portion, of such
payments would not be taxable to shareholders.

      After the end of the calendar year, shareholders will receive full
information on their dividends and capital gains distributions for tax
purposes. Shareholders will also be notified of their proportionate share of
long-term capital gains distributions that are eligible for a reduced rate of
tax under the Taxpayer Relief Act of 1997.

      To avoid being subject to a 31% federal backup withholding tax on taxable
dividends, capital gains distributions and the proceeds of redemptions and
repurchases, shareholders' taxpayer identification numbers must be furnished
and certified as to their accuracy.


      Dividends, interest and gains received by the Fund may give rise to
withholding and other taxes imposed by foreign countries. If it qualifies for
and has made the appropriate election with the Internal Revenue Service, the
Fund will report annually to its shareholders the amount per share of such
taxes, to enable shareholders to deduct their pro rata portion of such taxes
from their taxable income or claim United States foreign tax credits with
respect to such taxes. In the absence of such an election, the Fund would
deduct foreign tax in computing the amount of its distributable income.


      The foregoing discussion relates solely to the federal income tax
consequences of an investment in the Fund. Distributions may also be subject to
state and local taxes; therefore, each shareholder is advised to consult his or
her own tax advisor.

PERFORMANCE INFORMATION
- --------------------------------------------------------------------------------

From time to time the Fund may quote its "total return" in advertisements and
sales literature. These figures are computed separately for Class A, Class B,
Class C and Class D shares. The total return of the Fund is based on historical
earnings and is not intended to indicate future performance. The "average
annual total return" of the Fund refers to a figure reflecting the average
annualized percentage increase (or decrease) in the value of an initial
investment in a Class of the Fund of $1,000 over a period of one, five and ten
years, or over the life of the Fund, if less than any of the foregoing. Average
annual total return reflects all income earned by the Fund, any appreciation or
depreciation of the Fund's assets, all expenses incurred by the applicable
Class and all sales charges which would be incurred by shareholders, for the
stated periods. It also assumes reinvestment of all dividends and distributions
paid by the Fund.

      In addition to the foregoing, the Fund may advertise its total return for
each Class over different periods of time by means of aggregate, average, and
year-by-year or other types of total return figures. The Fund may also
advertise a growth of hypothetical investments of $10,000, $50,000 and $100,000
in each Class of shares of the Fund. Such calculations may or may not reflect
the deduction of any sales charge which, if reflected, would reduce the
performance quoted. The Fund from time to time may also advertise its
performance relative to certain performance rankings and indices compiled by
independent organizations (such as mutual fund performance rankings of Lipper
Analytical Services, Inc.).

ADDITIONAL INFORMATION
- -------------------------------------------------------------------------------

VOTING RIGHTS. All shares of beneficial interest of the Fund are of $0.01 par
value and are equal as to earnings, assets and voting privileges except that
each Class will have exclusive voting privileges with respect to matters
relating to distribution expenses borne solely by such Class or any other
matter in which the interests of one Class differ from the interests of any
other Class. In addition, Class B shareholders will have the right to vote on
any proposed material increase in Class A's expenses, if such proposal is
submitted separately to Class A shareholders. Also, as discussed herein, Class
A, Class B and Class C bear the expenses related to the distribution of their
respective shares.


      The Fund is not required to hold Annual Meetings of Shareholders and, in
ordinary circumstances, the Fund


28
<PAGE>

does not intend to hold such meetings. The Trustees may call Special Meetings
of Shareholders for action by shareholder vote as may be required by the Act or
the Declaration of Trust. The Trustees themselves have the power to alter the
number and the terms of office of the Trustees (as provided for in the
Declaration of Trust), and they may at any time lengthen or shorten their own
terms or make their terms of unlimited duration and appoint their own
successors, provided that always at least a majority of the Trustees has been
elected by the shareholders of the Fund. Under certain circumstances the
Trustees may be removed by action of the Trustees. The shareholders also have
the right under certain circumstances to remove the Trustees. The voting rights
of shareholders are not cumulative, so that holders of more than 50 percent of
the shares voting can, if they choose, elect all Trustees being elected, while
the holders of the remaining shares would be unable to elect any Trustees.

      Under Massachusetts law, shareholders of a business trust may, under
certain limited circumstances, be held personally liable as partners for the
obligations of the Fund. However, the Declaration of Trust contains an express
disclaimer of shareholder liability for acts or obligations of the Fund,
requires that Fund obligations include such disclaimer, and provides for
indemnification out of the Fund's property for any shareholder held personally
liable for the obligations of the Fund. Thus, the risk of a shareholder
incurring financial loss on account of shareholder liability is limited to
circumstances in which the Fund itself would be unable to meet its obligations.
Given the above limitations on shareholder personal liability, and the nature
of the Fund's assets and operations, the possibility of the Fund being unable
to meet its obligations is remote and, in the opinion of Massachusetts counsel
to the Fund, the risk to Fund shareholders of personal liability is remote.

CODE OF ETHICS. Directors, officers and employees of MSDW Advisors, MSDW
Services and MSDW Distributors are subject to a strict Code of Ethics adopted
by those companies. The Code of Ethics is intended to ensure that the interests
of shareholders and other clients are placed ahead of any personal interest,
that no undue personal benefit is obtained from a person's employment
activities and that actual and potential conflicts of interest are avoided. To
achieve these goals and comply with regulatory requirements, the Code of Ethics
requires, among other things, that personal securities transactions by
employees of the companies be subject to an advance clearance process to
monitor that no Morgan Stanley Dean Witter Fund is engaged at the same time in
a purchase or sale of the same security. The Code of Ethics bans the purchase
of securities in an initial public offering and prohibits engaging in futures
and options transactions and profiting on short-term trading (that is, a
purchase within sixty days of a sale or a sale within sixty days of a purchase)
of a security. In addition, investment personnel may not purchase or sell a
security for their personal account within thirty days before or after any
transaction in any Morgan Stanley Dean Witter Fund managed by them. Any
violations of the Code of Ethics are subject to sanctions, including reprimand,
demotion or suspension or termination of employment. The Code of Ethics
comports with regulatory requirements and the recommendations in the 1994
report by the Investment Company Institute Advisory Group on Personal
Investing.

MASTER/FEEDER CONVERSION. The Fund reserves the right to seek to achieve its
investment objective by investing all of its investable assets in a
non-diversified, open-end management investment company having the same
investment objective and policies and substantially the same investment
restrictions as those applicable to the Fund.

SHAREHOLDER INQUIRIES. All inquiries regarding the Fund should be directed to
the Fund at the telephone numbers or address set forth on the front cover of
this Prospectus.


                                                                             29
<PAGE>

MORGAN STANLEY DEAN WITTER
HEALTH SCIENCES TRUST
TWO WORLD TRADE CENTER
NEW YORK, NEW YORK 10048


TRUSTEES


Michael Bozic
Charles A. Fiumefreddo
Edwin J. Garn
John R. Haire
Wayne E. Hedien
Dr. Manuel H. Johnson
Michael E. Nugent
Philip J. Purcell
John L. Schroeder


OFFICERS

Charles A. Fiumefreddo
Chairman and Chief Executive Officer

Barry Fink
Vice President, Secretary and
General Counsel

Ronald J. Worobel
Vice President

Thomas F. Caloia
Treasurer


CUSTODIAN

The Bank of New York
90 Washington Street
New York, New York 10286


TRANSFER AGENT AND
DIVIDEND DISBURSING AGENT


Morgan Stanley Dean Witter Trust FSB
Harborside Financial Center
Plaza Two
Jersey City, New Jersey 07311


INDEPENDENT ACCOUNTANTS

PricewaterhouseCoopers LLP
1177 Avenue of the Americas
New York, New York 10036


INVESTMENT MANAGER

Morgan Stanley Dean Witter Advisors Inc.


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