MFS VARIABLE INSURANCE TRUST
497, 1997-05-05
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<PAGE>
 
<TABLE>
<S>                                          <C>
MFS-REGISTERED TRADEMARK- EMERGING GROWTH
SERIES
MFS-REGISTERED TRADEMARK- GROWTH WITH
INCOME SERIES                                PROSPECTUS
MFS-REGISTERED TRADEMARK- HIGH INCOME        May 1,
SERIES                                       1997
</TABLE>
 
- --------------------------------------------------------------------------------
 
<TABLE>
<S>                                                                <C>            <S>                                      <C>
MFS-Registered Trademark- VARIABLE INSURANCE TRUST-SM-
</TABLE>
 
MFS  Variable Insurance Trust (the "Trust") is an open-end management investment
company offering insurance company separate  accounts a selection of  investment
vehicles  for  variable  annuity  and  variable  life  insurance  contracts (the
"Contracts"). Currently the  Trust offers  shares of beneficial  interest of  12
separate  mutual fund series (individually  or collectively hereinafter referred
to as a "Series" or the "Series"),  three of which are offered pursuant to  this
Prospectus:
 
- -- MFS  EMERGING GROWTH  SERIES (the "Emerging  Growth Series"),  which seeks to
   provide long-term growth of capital;
 
- -- MFS GROWTH WITH INCOME SERIES (the "Growth With Income Series"), which  seeks
   to  provide reasonable  current income  and long-term  growth of  capital and
   income; and
 
- -- MFS HIGH INCOME SERIES (the "High  Income Series"), which seeks high  current
   income  by  investing  primarily  in  a  professionally  managed  diversified
   portfolio of  fixed  income securities,  some  of which  may  involve  equity
   features.
                              -------------------
 
THE HIGH INCOME SERIES MAY INVEST UP TO 100%, RESPECTIVELY, OF ITS NET ASSETS IN
LOWER  RATED BONDS, COMMONLY  KNOWN AS "JUNK BONDS,"  THAT ENTAIL GREATER RISKS,
INCLUDING DEFAULT RISKS, THAN THOSE FOUND IN HIGHER RATED SECURITIES.  INVESTORS
SHOULD  CAREFULLY CONSIDER  THESE RISKS  BEFORE INVESTING  (SEE "ADDITIONAL RISK
FACTORS -- LOWER RATED BONDS"). THE  EMERGING GROWTH SERIES AND THE GROWTH  WITH
INCOME  SERIES  ARE INTENDED  FOR INVESTORS  WHO UNDERSTAND  AND ARE  WILLING TO
ACCEPT THE RISKS  ENTAILED IN SEEKING  LONG-TERM GROWTH OF  CAPITAL. BECAUSE  OF
THEIR   INVESTMENT  POLICIES   PERMITTING  INVESTMENT   IN  FOREIGN  SECURITIES,
INVESTMENTS IN EACH  SERIES MAY  BE SUBJECT  TO A  GREATER DEGREE  OF RISK  THAN
INVESTMENTS  IN  OTHER INVESTMENT  COMPANIES WHICH  INVEST ENTIRELY  IN DOMESTIC
SECURITIES.
                              -------------------
 
  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.
                              -------------------
 
SHARES OF THE TRUST  ARE AVAILABLE AND  ARE BEING MARKETED  AS A POOLED  FUNDING
VEHICLE FOR LIFE INSURANCE COMPANIES WRITING ALL TYPES OF CONTRACTS.
 
This  Prospectus sets forth  concisely the information about  each Series that a
prospective investor should know  before applying for  the Contracts offered  by
the  separate accounts of certain  insurance companies ("Participating Insurance
Companies"). Investors are advised  to read this  Prospectus and the  applicable
Contract  prospectus  carefully and  retain them  for  future reference.  If you
require more detailed information, a  Statement of Additional Information  dated
May  1,  1997, as  amended or  supplemented from  time to  time (the  "SAI"), is
available upon  request without  charge and  may be  obtained by  calling or  by
writing to the Shareholder Servicing Agent (see back cover for address and phone
number).  The SAI, which is incorporated  by reference into this Prospectus, has
been filed with  the Securities  and Exchange  Commission (the  "SEC"). The  SEC
maintains  an Internet World Wide Web site that contains the SAI, materials that
are incorporated  by reference  into  this Prospectus  and  the SAI,  and  other
information  regarding the Series. This Prospectus is available on the Adviser's
Internet World Wide Web site at http://www.mfs.com.
 
   INVESTORS SHOULD READ THIS PROSPECTUS AND RETAIN IT FOR FUTURE REFERENCE.
<PAGE>
TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                                                                                       PAGE
                                                                                                       ---
  <S>                                                                                                  <C>
  1.  Expense Summary................................................................................   3
  2.  Investment Concept of the Trust................................................................   3
  3.  Condensed Financial Information................................................................   5
  4.  Investment Objectives and Policies.............................................................   8
      MFS Emerging Growth Series.....................................................................   8
      MFS Growth With Income Series..................................................................   8
      MFS High Income Series.........................................................................   9
  5.  Investment Techniques..........................................................................  10
  6.  Additional Risk Factors........................................................................  16
  7.  Management of the Series.......................................................................  18
  8.  Information Concerning Shares of Each Series...................................................  20
      Purchases and Redemptions......................................................................  20
      Net Asset Value................................................................................  20
      Distributions..................................................................................  21
      Tax Status.....................................................................................  21
      Description of Shares, Voting Rights and Liabilities...........................................  21
      Performance Information........................................................................  22
      Expenses.......................................................................................  22
      Shareholder Communications.....................................................................  23
  Appendix A -- Description of Bond Ratings..........................................................  A-1
  Appendix B -- Portfolio Composition Charts.........................................................  B-1
</TABLE>
 
                                       2
<PAGE>
1.  EXPENSE SUMMARY
 
ANNUAL OPERATING EXPENSES (AS A PERCENTAGE OF AVERAGE NET ASSETS):
 
<TABLE>
<CAPTION>
                                                                           MFS
                                                                MFS       GROWTH
                                                              EMERGING     WITH     MFS HIGH
                                                               GROWTH     INCOME     INCOME
                                                               SERIES     SERIES     SERIES
                                                              --------   --------   --------
<S>                                                           <C>        <C>        <C>
Management Fee..............................................  0.75%      0.75%      0.75%
Other Expenses (after expense limitation)(1)(2).............  0.25%      0.25%      0.25%
                                                              --------   --------    ---
Total Operating Expenses (after expense limitation)(2)......  1.00%      1.00%      1.00%
<FN>
- ------------------------
(1)        Each  Series has an expense offset  arrangement which reduces the Series' custodian  fee based upon the amount of
           cash maintained by the Series  with its custodian and  dividend disbursing agent, and  may enter into other  such
           arrangements  and directed  brokerage arrangements  (which would  also have  the effect  of reducing  the Series'
           expenses). Any such fee reductions are not reflected under "Other Expenses."
(2)        The Adviser has agreed to bear expenses for each Series, subject to reimbursement by each Series, such that  each
           Series'  "Other Expenses" shall not exceed 0.25% of the average daily net assets of the Series during the current
           fiscal year. See "Information Concerning Shares of  Each Series-- Expenses." Otherwise, "Other Expenses" for  the
           Emerging Growth Series, the Growth With Income Series and the High Income Series would be 0.41%, 1.32% and 0.87%,
           respectively, and "Total Operating Expenses" would be 1.16%, 2.07% and 1.62%, respectively, for these Series.
</TABLE>
 
    The   purpose  of  the  expense  table  above  is  to  assist  investors  in
understanding the various costs  and expenses that a  shareholder of the  Series
will  bear directly or indirectly. The  Series' annual operating expenses do not
reflect  expenses  imposed  by  separate  accounts  of  Participating  Insurance
Companies  through which  an investment  in a  Series is  made or  their related
Contracts. A separate account's expenses are disclosed in the prospectus through
which the Contract relating to that separate account is offered for sale.
 
2.  INVESTMENT CONCEPT OF THE TRUST
 
    The Trust is an open-end, registered management investment company comprised
of the following twelve series:  Emerging Growth Series, Value Series,  Research
Series,  Growth With Income Series, Total  Return Series, Utilities Series, High
Income Series, World  Governments Series,  Strategic Fixed  Income Series,  Bond
Series,  Limited  Maturity Series  and  Money Market  Series.  Each Series  is a
segregated, separately  managed  portfolio of  securities.  All of  the  Series,
except the Utilities Series, World Governments Series and Strategic Fixed Income
Series, are diversified. Additional series may be created from time to time. The
Trust  was organized as a  business trust under the  laws of The Commonwealth of
Massachusetts by a Declaration of Trust dated February 1, 1994.
 
    The Trust  currently  offers shares  of  each Series  to  insurance  company
separate  accounts that fund Contracts. Separate accounts may purchase or redeem
shares at  net asset  value without  any sales  or redemption  charge. Fees  and
charges imposed by a separate account, however, will affect the actual return to
the   holder  of  a  Contract.  A  separate  account  may  also  impose  certain
restrictions or limitations on the  allocation of purchase payments or  Contract
value  to one or more Series, and not  all Series may be available in connection
with a particular Contract. Prospective investors should consult the  applicable
Contract  prospectus for information regarding fees and expenses of the Contract
and separate account and any  applicable restrictions or limitations. The  Trust
assumes no responsibility for such prospectuses.
 
    Shares  of the Series are offered  to the separate accounts of Participating
Insurance Companies  that are  affiliated  or unaffiliated  ("shared  funding").
Shares  of the Series may serve as  the underlying investments for both variable
annuity  and  variable  life  insurance  contracts  ("mixed  funding").  Due  to
differences  in tax treatment or other  considerations, the interests of various
Contract owners might at some time be in conflict. The Trust currently does  not
foresee  any such conflict. Nevertheless, the Trust's Trustees intend to monitor
events in  order to  identify any  material irreconcilable  conflicts which  may
possibly arise and to determine what action, if any, should be taken in response
thereto.  If such a conflict were to occur, one or more separate accounts of the
Participating Insurance Companies might be required to withdraw its  investments
in  one one  or more  Series. This might  force a  Series to  sell securities at
disadvantageous prices.
 
    Individual Contract holders are not the "shareholders" of the Trust. Rather,
the Participating  Insurance  Companies  and their  separate  accounts  are  the
shareholders  or  investors, although  such  companies may  pass  through voting
rights to their Contract holders.
 
                                       3
<PAGE>
    The Trust's Board of Trustees provides broad supervision over the affairs of
the Trust and the Series.  Massachusetts Financial Services Company, a  Delaware
corporation  ("MFS" or the "Adviser"), is the investment adviser to each Series.
A majority of the Trustees of the Trust are not affiliated with the Adviser. The
Adviser is responsible for the management of  the assets of each Series and  the
officers  of the Trust  are responsible for the  operations. The Adviser manages
the Series'  portfolios  from day  to  day  in accordance  with  the  investment
objectives and policies of each Series. The selection of investments and the way
they  are managed  depend on the  conditions and  trends in the  economy and the
financial marketplaces.
 
                                       4
<PAGE>
3.  CONDENSED FINANCIAL INFORMATION
 
The following financial information (presented  for each Series which  commenced
investment  operations prior  to December 31,  1996) has been  audited since the
commencement of  investment operations  of such  Series and  should be  read  in
conjunction with the financial statements included in the Series' Annual Reports
to  Shareholders. These financial statements  are incorporated by reference into
the SAI in reliance  upon the report of  the Series' independent auditors  given
upon  their authority as experts in accounting and auditing. The Series' current
independent auditors are Deloitte & Touche LLP.
 
                             EMERGING GROWTH SERIES
 
<TABLE>
<CAPTION>
                                                                      YEAR ENDED          PERIOD ENDED
                                                                   DECEMBER 31, 1996   DECEMBER 31, 1995*
                                                                   -----------------   ------------------
<S>                                                                <C>                 <C>
Per share data (for a share outstanding throughout each period):
Net asset value--beginning of period.............................      $  11.41             $10.00
                                                                       --------             ------
Income from investment operations#--
  Net investment income (loss)Section............................      $  (0.01)            $ 0.01
  Net realized and unrealized gain on investments and foreign
    currency transactions........................................          1.95               1.74
                                                                       --------             ------
    Total from investment operations.............................      $   1.94             $ 1.75
                                                                       --------             ------
Less distributions declared to shareholders--
  From net investment income.....................................      $     --             $(0.01)
  From net realized gain on investments and foreign currency
    transactions.................................................         (0.06)             (0.26)
  In excess of net realized gain on investments and foreign
    currency transactions........................................         (0.05)                --
  Tax return of capital..........................................            --              (0.07)
                                                                       --------             ------
    Total distributions declared to shareholders.................      $  (0.11)            $(0.34)
                                                                       --------             ------
Net asset value--end of period...................................      $  13.24             $11.41
                                                                       --------             ------
                                                                       --------             ------
Total return.....................................................         17.02%             17.41%++
Ratios (to average net assets)/Supplemental dataSection:
  Expenses.......................................................          1.00%              1.00%+
  Net investment income (loss)...................................         (0.08)%             0.10%+
Portfolio turnover...............................................            96%                73%
Average commission rate###.......................................      $ 0.0401                 --
Net assets at end of period (000 omitted)........................      $104,956             $3,869
- ---------
        * For the period from the commencement of investment operations, July 24, 1995 to December 31, 1995.
        +  Annualized.
       ++  Not annualized.
        #  Per share data is based on average shares outstanding.
      ###  Average commission rate is calculated for Series' with fiscal years beginning on or after September 1, 1995.
  Section  The Adviser voluntarily agreed to maintain the expenses of the Series at not more than 1.00% of average daily
           net assets. To the extent actual expenses were over these limitations, the net investment loss per share  and
           the ratios would have been:
 
Net investment loss..............................................         $(0.03)           $(0.18)
Ratios (to average net assets):
  Expenses.......................................................           1.16%             2.91%+
  Net investment loss............................................          (0.23)%           (1.78)%+
</TABLE>
 
                                       5
<PAGE>
                           GROWTH WITH INCOME SERIES
 
<TABLE>
<CAPTION>
                                                                       YEAR ENDED           PERIOD ENDED
                                                                    DECEMBER 31, 1996    DECEMBER 31, 1995*
                                                                   -------------------   ------------------
<S>                                                                <C>                   <C>
Per share data (for a share outstanding throughout each period):
Net asset value--beginning of period.............................        $ 10.61               $10.00
                                                                         -------               ------
Income from investment operations#--
  Net investment incomeSection...................................        $  0.18               $ 0.05
  Net realized and unrealized gain on investments and foreign
    currency transactions........................................           2.42                 0.61
                                                                         -------               ------
    Total from investment operations.............................        $  2.60               $ 0.66
                                                                         -------
Less distributions declared to shareholders--
  From net investment income.....................................        $ (0.09)              $(0.05)
  From net realized gain on investments and foreign currency
    transactions.................................................          (0.13)                  --
  In excess of net realized gain on investments and foreign
    currency transactions........................................          (0.01)                  --
                                                                         -------               ------
    Total distributions declared to shareholders.................        $ (0.23)              $(0.05)
                                                                         -------               ------
Net asset value--end of period...................................        $ 12.98               $10.61
                                                                         -------               ------
                                                                         -------               ------
Total return.....................................................          24.46%                6.64%++
Ratios (to average net assets)/Supplemental dataSection:
  Expenses.......................................................           1.00%                1.00%+
  Net investment income..........................................           1.52%                2.20%+
Portfolio turnover...............................................             41%                   2%
Average commission rate###.......................................        $0.0351                   --
Net assets at end of period (000 omitted)........................        $ 9,174               $  365
<FN>
- ------------------------
        *  For the period from the commencement of investment operations, October 9, 1995 to December 31, 1995.
        +  Annualized.
       ++  Not annualized.
        #  Per share data is based on average shares outstanding.
      ###  Average commission rate is calculated for funds with fiscal years beginning on or after September 1, 1995.
  Section  The Adviser voluntarily agreed to maintain the expenses of the Series at not more than 1.00% of average daily
           net  assets. To the extent actual expenses were over  these limitations, the net investment income (loss) per
           share and the ratios would have been:
 
Net investment income (loss).....................................            $0.05          $ (0.41)
Ratios (to average net assets):
  Expenses.......................................................             2.07%           21.44%+
  Net investment income (loss)...................................             0.46%          (18.24)%+
</TABLE>
 
                                       6
<PAGE>
                               HIGH INCOME SERIES
 
<TABLE>
<CAPTION>
                                                                       YEAR ENDED           PERIOD ENDED
                                                                    DECEMBER 31, 1996    DECEMBER 31, 1995*
                                                                   -------------------   ------------------
<S>                                                                <C>                   <C>
Per share data (for a share outstanding throughout each period):
Net asset value--beginning of period.............................        $ 10.29               $10.00
                                                                         -------               ------
Income from investment operations#--
  Net investment incomeSection...................................        $  0.89               $ 0.34
  Net realized and unrealized gain on investments................           0.32                 0.18
                                                                         -------               ------
    Total from investment operations.............................        $  1.21               $ 0.52
                                                                         -------               ------
Less distributions declared to shareholders--
  From net investment income.....................................        $ (0.53)              $(0.23)
  From net realized gain on investments..........................          (0.10)                  --
                                                                         -------               ------
    Tota distributions declared to shareholders..................        $ (0.63)              $(0.23)
                                                                         -------               ------
Net asset value--end of period...................................        $ 10.87               $10.29
                                                                         -------               ------
                                                                         -------               ------
Total return.....................................................          11.80%                5.25%++
Ratios (to average net assets)/Supplemental dataSection:
  Expenses.......................................................           1.00%                1.00%+
  Net investment income..........................................           8.18%                8.17%+
Portfolio turnover...............................................            135%                  32%
Net assets at end of period (000 omitted)........................        $12,994               $1,946
<FN>
- ------------------------
        *  For the period from the commencement of investment operations, July 26, 1995 to December 31, 1995.
        +  Annualized.
       ++  Not annualized.
        #  Per share data is based on average shares outstanding.
  Section  The Adviser voluntarily agreed to maintain  the expenses of the Series at  not more than 1.00% of average  daily
           net  assets. To the extent actual expenses were over  these limitations, the net investment income per share and
           the ratios would have been:
 
Net investment income............................................        $0.82            $0.20
Ratios (to average net assets):
  Expenses.......................................................         1.62%            4.38%+
  Net investment income..........................................         7.56%            4.82%+
</TABLE>
 
                                       7
<PAGE>
4.  INVESTMENT OBJECTIVES AND POLICIES
 
    Each Series has  different investment  objectives which  it pursues  through
separate  investment policies, as described below. The differences in objectives
and policies among the Series can be expected to affect the degree of market and
financial risk to which each  Series is subject and  the return of each  Series.
The  investment objectives  and policies  of each  Series may,  unless otherwise
specifically stated, be changed by the Trustees  of the Trust without a vote  of
the  shareholders. Any investment  involves risk and there  is no assurance that
the objectives of any Series will be achieved.
 
    In addition  to  the specific  investment  practices described  below,  each
Series  may also engage in certain  investment techniques as described under the
caption  "Investment  Techniques"  below  and  in  the  SAI  under  the  caption
"Investment  Techniques." The Series' investments  are subject to certain risks,
as described in the above-referenced sections of this Prospectus and the SAI and
as described below under the caption "Additional Risk Factors."
 
MFS EMERGING GROWTH SERIES  -- The Series seeks  to provide long-term growth  of
capital.  Dividend and  interest income  from portfolio  securities, if  any, is
incidental to the Series' investment objective of long-term growth of capital.
 
    The Series' policy is to invest primarily (I.E., at least 80% of its  assets
under  normal circumstances) in common stocks of companies that MFS believes are
early in  their  life  cycle  but  which have  the  potential  to  become  major
enterprises  (emerging  growth  companies). Such  companies  generally  would be
expected to show earnings growth over time that is well above the growth rate of
the overall economy  and the  rate of inflation,  and would  have the  products,
technologies,  management and market  and other opportunities  which are usually
necessary to become more widely recognized as growth companies. Emerging  growth
companies  can be  of any  size, and  the Series  may invest  in larger  or more
established companies whose rates of earnings growth are expected to  accelerate
because  of  special  factors,  such as  rejuvenated  management,  new products,
changes in consumer demand, or basic changes in the economic environment.  While
the  Series will invest primarily in common stocks, the Series may, to a limited
extent, seek appreciation  in other  types of  securities such  as fixed  income
securities  (which  may be  unrated), convertible  securities and  warrants when
relative values  make  such purchases  appear  attractive either  as  individual
issues  or as types  of securities in certain  economic environments. The Series
may  invest  in  non-convertible  fixed  income  securities  rated  lower   than
"investment  grade"  (rated  Ba  or lower  by  Moody's  Investors  Service, Inc.
("Moody's") or BB  or lower  by Standard &  Poor's Ratings  Services ("S&P")  or
Fitch  Investors Service, Inc. ("Fitch")) (commonly known as "junk bonds") or in
comparable unrated securities,  when, in  the opinion  of the  Adviser, such  an
investment  presents a greater opportunity for appreciation with comparable risk
to  an  investment  in  "investment  grade"  securities.  Under  normal   market
conditions,  the Series will invest not more than  5% of its net assets in these
securities. For  a  description  of  these  ratings,  see  Appendix  A  to  this
Prospectus.
 
    The  nature of investing in emerging  growth companies involves greater risk
than is customarily associated with  investments in more established  companies.
Emerging growth companies often have limited product lines, markets or financial
resources,  and they  may be  dependent on  one-person management.  In addition,
there may be less  research available on many  promising small and medium  sized
emerging  growth companies, making  it more difficult to  find and analyze these
companies.  The  securities  of  emerging  growth  companies  may  have  limited
marketability and may be subject to more abrupt or erratic market movements than
securities  of larger, more established growth  companies or the market averages
in general. Shares of the Series, therefore, are subject to greater  fluctuation
in  value than shares  of a conservative equity  fund or of  a growth fund which
invests entirely in proven growth stocks.
 
    Consistent with its investment objective  and policies described above,  the
Series  may also invest up to 25% (and generally expects to invest not more than
15%) of  its  net  assets  in  foreign  securities  (including  emerging  market
securities and Brady Bonds) which are not traded on a U.S. exchange.
 
MFS  GROWTH  WITH INCOME  SERIES --  The Growth  With Income  Series' investment
objectives are  to provide  reasonable current  income and  long-term growth  of
capital and income.
 
    Under normal market conditions, the Growth With Income Series will invest at
least  65% of its assets in equity  securities of companies that are believed to
have long-term prospects for growth and  income. Equity securities in which  the
Series  may invest  include the following:  common stocks,  preferred stocks and
preference stocks;  securities  such  as  bonds, warrants  or  rights  that  are
convertible  into stocks;  and depositary  receipts for  those securities. These
securities  may  be   listed  on   securities  exchanges,   traded  in   various
over-the-counter markets or have no organized markets.
 
                                       8
<PAGE>
    Consistent  with its investment objective  and policies described above, the
Series may also invest up to 75% (and generally expects to invest not more  than
15%)  of  its  net  assets  in  foreign  securities  (including  emerging market
securities and Brady Bonds) which are not traded on a U.S. exchange.
 
MFS HIGH INCOME SERIES -- The investment objective of the High Income Series  is
to  seek high current income by  investing primarily in a professionally managed
diversified portfolio  of fixed  income securities,  some of  which may  involve
equity features.
 
    Fixed  income securities offering the high current income sought by the High
Income Series  normally include  those  fixed income  securities which  offer  a
current  yield above  that generally available  on debt securities  in the three
highest rating categories of the  recognized rating agencies (commonly known  as
"junk  bonds" if  rated below the  four highest categories  of recognized rating
agencies). The  Series  may  invest  up  to 100%  of  its  net  assets  in  such
securities. For a description of these rating categories, see Appendix A to this
Prospectus  and Appendix  C for  a chart showing  the Series'  holdings of fixed
income securities broken  down by  rating category  as of  the end  of its  most
recent  fiscal  year.  (See  "Additional Risk  Factors"  below.)  However, since
available yields and yield  differentials vary over time,  no specific level  of
income  or yield  differential can  ever be assured.  The dividends  paid by the
Series will  increase or  decrease in  relation to  the income  received by  the
Series  from its investments, which would in any case be reduced by the expenses
of the Series before such income is distributed to its shareholders.
 
    Fixed income  securities include  preferred and  preference stocks  and  all
types  of debt obligations of both domestic  and foreign issuers, such as bonds,
debentures, notes, equipment  lease certificates,  equipment trust  certificates
(including interests in trusts or other entities representing such obligations),
conditional   sales  contracts,  commercial  paper  and  obligations  issued  or
guaranteed by  the U.S.  Government,  any foreign  government  or any  of  their
respective  political  subdivisions,  agencies  or  instrumentalities (including
obligations, such as repurchase agreements, secured by instruments).
 
    Corporate debt securities may bear fixed, fixed and contingent, or  variable
rates  of  interest  and may  involve  equity  features, such  as  conversion or
exchange rights  or warrants  for the  acquisition of  stock of  the same  or  a
different  issuer; participations  based on revenues,  sales or  profits; or the
purchase of common stock in a unit transaction (where corporate debt  securities
and  common stock are  offered as a  unit). Under normal  market conditions, not
more than 25% of the value of the total assets of the High Income Series will be
invested in equity securities, including common stocks, warrants and rights.
 
    Consistent with its investment objective  and policies described above,  the
Series  may also invest up to 25% (and generally expects to invest not more than
10%) of  its  net  assets  in  foreign  securities  (including  emerging  market
securities  and Brady Bonds) which are not traded on a U.S. exchange. The Series
has authority to invest up  to 25% of its total  assets in securities issued  or
guaranteed  by foreign governments or  their agencies or instrumentalities. (See
"Additional Risk Factors" below.)
 
    The High Income Series may invest up to 40% of the value of its total assets
in each of the  electric utility and telephone  industries, but will not  invest
more  than 25% in  either of those  industries unless yields  available for four
consecutive weeks in the  four highest rating categories  on new issue bonds  in
such  industry (issue size  of $50 million  or more) have  averaged in excess of
105% of yields of  new issue long-term industrial  bonds similarly rated  (issue
size  of $50 million or  more) and, in the opinion  of the Adviser, the relative
return available  from  the  electric  utility or  telephone  industry  and  the
relative  risk, marketability,  quality and  availability of  securities of such
industry justifies such an investment.
 
    When and  if  available, fixed  income  securities  may be  purchased  at  a
discount  from face value.  However, the High  Income Series does  not intend to
hold such securities to maturity for the purpose of achieving potential  capital
gains, unless current yields on these securities remain attractive. From time to
time the Series may purchase securities not paying interest at the time acquired
if, in the opinion of the Adviser, such securities have the potential for future
income or capital appreciation.
 
                                       9
<PAGE>
5.  INVESTMENT TECHNIQUES
 
    LENDING OF PORTFOLIO SECURITIES: Each of the Series may seek to increase its
income  by  lending portfolio  securities. Such  loans will  usually be  made to
member firms (and  subsidiaries thereof)  of the  New York  Stock Exchange  (the
"Exchange")  and to  member banks  of the Federal  Reserve System,  and would be
required to  be  secured  continuously  by collateral  in  cash,  U.S.  Treasury
securities  or an irrevocable letter of credit  maintained on a current basis at
an amount at least equal  to the market value of  the securities loaned. If  the
Adviser  determines to make securities  loans, it is intended  that the value of
the securities loaned would not exceed 10% of the value of the net assets of the
Series making the loans.
 
    EMERGING MARKET  SECURITIES: Consistent  with their  respective  objectives,
each  Series may invest in securities  of issuers whose principal activities are
located in  emerging market  countries. Emerging  market countries  include  any
country  determined by  the Adviser to  have an emerging  market economy, taking
into account a number of  factors, including whether the  country has a low-  to
middle-  income economy according  to the International  Bank for Reconstruction
and Development, the country's foreign  currency debt rating, its political  and
economic stability and the development of its financial and capital markets. The
Adviser  determines whether an  issuer's principal activities  are located in an
emerging  market  country  by  considering  such  factors  as  its  country   of
organization,  the principal trading market for its securities and the source of
its revenues and assets. The issuer's principal activities generally are  deemed
to  be  located  in a  particular  country if:  (a)  the security  is  issued or
guaranteed by the government of that country or any of its agencies, authorities
or instrumentalities;  (b)  the issuer  is  organized  under the  laws  of,  and
maintains  a principal office in that country;  (c) the issuer has its principal
securities trading market in that country; (d) the issuer derives 50% or more of
its total revenues from goods sold or services performed in that country; or (e)
the issuer has 50% or more of its assets in that country.
 
    BRADY BONDS:  Each  of the  Series  may invest  in  Brady Bonds,  which  are
securities  created through  the exchange of  existing commercial  bank loans to
public and  private  entities in  certain  emerging  markets for  new  bonds  in
connection  with debt restructurings under  a debt restructuring plan introduced
by former U.S. Secretary of the Treasury, Nicholas F. Brady (the "Brady  Plan").
Brady  Plan  debt restructurings  have been  implemented  to date  in Argentina,
Brazil, Bulgaria,  Costa  Rica,  Dominican Republic,  Ecuador,  Jordan,  Mexico,
Nigeria,  Panama, the  Philippines, Poland,  Uruguay and  Venezuela. Brady Bonds
have been issued only recently, and for  that reason do not have a long  payment
history.  Brady Bonds may  be collateralized or  uncollateralized, are issued in
various currencies (but primarily  the U.S. dollar) and  are actively traded  in
over-the-counter  secondary  markets.  U.S.  dollar-denominated,  collateralized
Brady Bonds, which may be fixed-rate bonds or floating-rate bonds, are generally
collateralized in full as to principal by U.S. Treasury zero coupon bonds having
the same maturity as the bonds. Brady Bonds are often viewed as having three  or
four  valuation components: the  collateralized repayment of  principal at final
maturity; the collateralized  interest payments;  the uncollateralized  interest
payments;  and any  uncollateralized repayment  of principal  at maturity (these
uncollateralized amounts  constituting the  "residual risk").  In light  of  the
residual  risk of Brady Bonds  and the history of  defaults of countries issuing
Brady Bonds  with  respect  to  commercial bank  loans  by  public  and  private
entities, investments in Brady Bonds may be viewed as speculative.
 
    REPURCHASE  AGREEMENTS:  Each  of  the  Series  may  enter  into  repurchase
agreements in order to earn income on available cash or as a temporary defensive
measure. Under a repurchase agreement,  a Series acquires securities subject  to
the  seller's agreement  to repurchase  at a  specified time  and price.  If the
seller becomes subject to a proceeding  under the bankruptcy laws or its  assets
are  otherwise  subject to  a stay  order,  the Series'  right to  liquidate the
securities may be  restricted (during  which time  the value  of the  securities
could  decline).  As  discussed in  the  SAI,  each Series  has  adopted certain
procedures intended to minimize risk.
 
    "WHEN-ISSUED" SECURITIES: Each of  the Series may  purchase securities on  a
"when-issued"  or on a "forward delivery" basis, which means that the securities
will be  delivered to  the Series  at  a future  date usually  beyond  customary
settlement time. The commitment to purchase a security for which payment will be
made  on a future date  may be deemed a separate  security. In general, a Series
does not pay  for such  securities until received,  and does  not start  earning
interest on the securities until the contractual settlement date. While awaiting
delivery of securities purchased on such bases, a Series will normally invest in
liquid assets.
 
                                       10
<PAGE>
    MORTGAGE  "DOLLAR ROLL" TRANSACTIONS: The High  Income Series may enter into
mortgage "dollar  roll"  transactions  with selected  banks  and  broker-dealers
pursuant  to which a Series sells mortgage-backed securities for delivery in the
future (generally within  30 days)  and simultaneously  contracts to  repurchase
substantially similar (same type, coupon and maturity) securities on a specified
future  date.  The  Series  record  these  transactions  as  sale  and  purchase
transactions, rather than as  borrowing transactions. A  Series will only  enter
into covered rolls. A "covered roll" is a specific type of dollar roll for which
there  is an  offsetting cash  position or  a cash  equivalent security position
which matures  on or  before the  forward  settlement date  of the  dollar  roll
transaction.  In the  event that  the party  with whom  the Series  contracts to
replace substantially similar securities on a future date fails to deliver  such
securities,  the Series may not  be able to obtain  such securities at the price
specified in such contract and thus may not benefit from the price  differential
between the current sales price and the repurchase price.
 
    RESTRICTED  SECURITIES: Each  of the Series  (except the  Growth With Income
Series) may purchase securities that are not registered under the Securities Act
of 1933 (the "1933 Act") ("restricted securities"), including those that can  be
offered  and sold to "qualified institutional  buyers" under Rule 144A under the
1933 Act  ("Rule  144A  securities").  A determination  is  made  based  upon  a
continuing  review of  the trading  markets for  a specific  Rule 144A security,
whether such security is liquid and  thus not subject to the Series'  limitation
on  investing not more than  15% of its net  assets in illiquid investments. The
Board of Trustees has adopted guidelines and delegated to MFS the daily function
of determining and monitoring the liquidity of Rule 144A securities. The  Board,
however, retains oversight, focusing on factors such as valuation, liquidity and
availability  of information. Investing  in Rule 144A  securities could have the
effect of decreasing  the level  of liquidity  in a  Series to  the extent  that
qualified institutional buyers become for a time uninterested in purchasing Rule
144A securities held in the Series' portfolio.
 
    CORPORATE  ASSET-BACKED SECURITIES: Each  of the Emerging  Growth Series and
the High Income Series  may invest in  corporate asset-backed securities.  These
securities,  issued by trusts and special  purpose corporations, are backed by a
pool  of  assets,  such  as   credit  card  and  automobile  loan   receivables,
representing the obligations of a number of different parties.
 
    Corporate  asset-backed securities  present certain risks.  For instance, in
the case of credit card receivables,  these securities may not have the  benefit
of  any security interest in the related collateral. Credit card receivables are
generally unsecured and the debtors are  entitled to the protection of a  number
of  state and federal consumer credit laws,  many of which give such debtors the
right to set off certain amounts owed on the credit cards, thereby reducing  the
balance  due. Most  issuers of  automobile receivables  permit the  servicers to
retain possession of the  underlying obligations. If the  servicer were to  sell
these  obligations to another  party, there is  a risk that  the purchaser would
acquire an interest superior  to that of the  holders of the related  automobile
receivables.  In addition, because of the large number of vehicles involved in a
typical issuance and technical  requirements under state  laws, the trustee  for
the  holders  of  the automobile  receivables  may  not have  a  proper security
interest in all of the obligations backing such receivables. Therefore, there is
the possibility  that recoveries  on  repossessed collateral  may not,  in  some
cases,  be available  to support  payments on  these securities.  The underlying
assets  (E.G.,  loans)  are  also  subject  to  prepayments  which  shorten  the
securities' weighted average life and may lower their return.
 
    Corporate  asset-backed  securities are  often backed  by  a pool  of assets
representing the obligations  of a number  of different parties.  To lessen  the
effect  of  failures by  obligors  on underlying  assets  to make  payments, the
securities  may  contain  elements  of  credit  support  which  fall  into   two
categories:  (i)  liquidity  protection;  and  (ii)  protection  against  losses
resulting from  ultimate  default  by  an  obligor  on  the  underlying  assets.
Liquidity  protection  refers to  the provision  of  advances, generally  by the
entity administering the pool of assets, to ensure that the receipt of  payments
on  the underlying  pool occurs in  a timely fashion.  Protection against losses
resulting from ultimate  default ensures payment  through insurance policies  or
letters of credit obtained by the issuer or sponsor from third parties. A Series
will  not pay any additional or separate  fees for credit support. The degree of
credit support  provided  for  each  issue  is  generally  based  on  historical
information  respecting the level of credit  risk associated with the underlying
assets. Delinquency or  loss in  excess of that  anticipated or  failure of  the
credit  support could  adversely affect  the return on  an investment  in such a
security.
 
    ZERO COUPON BONDS, DEFERRED  INTEREST BONDS AND PIK  BONDS: The Growth  With
Income  Series and the High  Income Series may invest  in zero coupon bonds. The
High  Income  Series  may  also  invest  in  deferred  interest  bonds  and  PIK
 
                                       11
<PAGE>
bonds.  Zero coupon and  deferred interest bonds are  debt obligations which are
issued or purchased  at a  significant discount  from face  value. The  discount
approximates  the total  amount of interest  the bonds will  accrue and compound
over the period until maturity or the  first interest payment date at a rate  of
interest  reflecting the market  rate of the  security at the  time of issuance.
While zero  coupon  bonds do  not  require  the periodic  payment  of  interest,
deferred interest bonds provide for a period of delay before the regular payment
of interest begins. PIK bonds are debt obligations which provide that the issuer
thereof may, at its option, pay interest on such bonds in cash or in the form of
additional  debt obligations. Such investments  benefit the issuer by mitigating
its need for cash to meet debt service, but also require a higher rate of return
to attract  investors  who are  willing  to defer  receipt  of such  cash.  Such
investments  may experience greater volatility in market value due to changes in
interest rates than debt  obligations which make  regular payments of  interest.
The  Series  will  accrue income  on  such  investments for  tax  and accounting
purposes, as required, which is distributable to shareholders and which, because
no cash is received at the time of accrual, may require the liquidation of other
portfolio securities to satisfy the Series' distribution obligations.
 
    COLLATERALIZED MORTGAGE OBLIGATIONS AND MULTICLASS PASS-THROUGH  SECURITIES:
The  High Income  Series may  invest a portion  of its  assets in collateralized
mortgage obligations or  "CMOs," which  are debt  obligations collateralized  by
mortgage   loans  or  mortgage  pass-through  securities.  Typically,  CMOs  are
collateralized by certificates  issued by  GNMA, the  Federal National  Mortgage
Association  ("FNMA") or the  Federal Home Loan  Mortgage Corporation ("FHLMC"),
but also may be collateralized by  whole loans or private mortgage  pass-through
securities  (such collateral collectively referred to as "Mortgage Assets"). The
Series may  also invest  a  portion of  its  assets in  multiclass  pass-through
securities  which are  interests in  a trust  composed of  Mortgage Assets. CMOs
(which include multiclass  pass-through securities) may  be issued by  agencies,
authorities   or  instrumentalities  of  the   U.S.  Government  or  by  private
originators of,  or investors  in, mortgage  loans, including  savings and  loan
associations,  mortgage banks,  commercial banks,  investment banks  and special
purpose subsidiaries of the foregoing. Payments of principal of and interest  on
the  Mortgage Assets, and any reinvestment  income thereon, provide the funds to
pay debt service on the CMOs  or make scheduled distributions on the  multiclass
pass-through securities. In a CMO, a series of bonds or certificates are usually
issued  in multiple classes with different maturities. Each class of CMOs, often
referred to as a  "tranche," is issued  at a specific  fixed or floating  coupon
rate and has a stated maturity or final distribution date. Principal prepayments
on  the Mortgage Assets may  cause the CMOs to  be retired substantially earlier
than their stated maturities or final distribution dates, resulting in a loss of
all or part of the  premium if any has been  paid. Certain classes of CMOs  have
priority  over  others  with  respect  to  the  receipt  of  prepayments  on the
mortgages. Therefore, depending on the type  of CMOs in which a Series  invests,
the  investment may be subject  to a greater or  lesser risk of prepayments than
other types of mortgage-related securities.
 
    The High Income  Series may  also invest in  parallel pay  CMOs and  Planned
Amortization  Class  CMOs ("PAC  Bonds"). Parallel  pay  CMOs are  structured to
provide payments of principal on each payment  date to more than one class.  PAC
Bonds  generally require  payments of  a specified  amount of  principal on each
payment date. PAC Bonds are always parallel pay CMOs with the required principal
payment on such securities having the  highest priority after interest has  been
paid  to all classes. For  a further description of  CMOs, parallel pay CMOs and
PAC Bonds and the risks related to transactions therein, see the SAI.
 
    STRIPPED MORTGAGE-BACKED SECURITIES:  The High  Income Series  may invest  a
portion of its assets in stripped mortgage-backed securities ("SMBS"), which are
derivative  multiclass mortgage  securities usually structured  with two classes
that receive different proportions of interest and principal distributions  from
an underlying pool of mortgage assets. For a further description of SMBS and the
risks related to transactions therein, see the SAI.
 
    LOAN  PARTICIPATIONS  AND OTHER  DIRECT INDEBTEDNESS:  Each of  the Emerging
Growth Series and the High Income Series  may invest a portion of its assets  in
"loan  participations"  and  other  direct indebtedness.  By  purchasing  a loan
participation, a Series acquires some or all of the interest of a bank or  other
lending  institution in  a loan  to a  corporate borrower.  Many such  loans are
secured, and  most  impose  restrictive  covenants which  must  be  met  by  the
borrower.  These loans are  made generally to  finance internal growth, mergers,
acquisitions,  stock  repurchases,  leveraged   buy-outs  and  other   corporate
activities.  Such loans may be in default at  the time of purchase. A Series may
also purchase other direct  indebtedness such as trade  or other claims  against
companies,  which generally represent money owed by the company to a supplier of
goods and  services. These  claims may  also be  purchased at  a time  when  the
company  is  in default.  Certain of  the loan  participations and  other direct
indebtedness acquired by  a Series  may involve revolving  credit facilities  or
other  standby financing commitments  which obligate a  Series to pay additional
cash on a certain date or on demand.
 
                                       12
<PAGE>
    The highly leveraged nature of many such loans and other direct indebtedness
may  make such  loans especially  vulnerable to  adverse changes  in economic or
market conditions. Loan participations and other direct indebtedness may not  be
in  the form of  securities or may  be subject to  restrictions on transfer, and
only limited opportunities may exist to resell such instruments. As a result,  a
Series  may be unable to sell such investments  at an opportune time or may have
to resell them at less than fair market value. For a further discussion of  loan
participations,  other direct indebtedness and the risks related to transactions
therein, see the SAI.
 
    MORTGAGE PASS-THROUGH  SECURITIES:  The High  Income  Series may  invest  in
mortgage   pass-through   securities.  Mortgage   pass-through   securities  are
securities representing interests in "pools" of mortgage loans. Monthly payments
of interest and principal  by the individual borrowers  on mortgages are  passed
through  to the  holders of the  securities (net of  fees paid to  the issuer or
guarantor of the securities) as the  mortgages in the underlying mortgage  pools
are  paid off. Payment  of principal and interest  on some mortgage pass-through
securities (but  not the  market  value of  the  securities themselves)  may  be
guaranteed  by the full faith and credit of  the U.S. Government (in the case of
securities guaranteed  by  GNMA);  or guaranteed  by  U.S.  Government-sponsored
corporations   (such  as  FNMA  or  FHLMC,  which  are  supported  only  by  the
discretionary  authority  of  the  U.S.  Government  to  purchase  the  agency's
obligations).   Mortgage  pass-through   securities  may   also  be   issued  by
non-governmental  issuers   (such  as   commercial  banks,   savings  and   loan
institutions,  private mortgage insurance companies,  mortgage bankers and other
secondary market  issuers).  See the  SAI  for  a further  discussion  of  these
securities.
 
    INDEXED  SECURITIES: The High Income Series may invest in indexed securities
whose value  is  linked  to foreign  currencies,  interest  rates,  commodities,
indices  or other  financial indicators.  Most indexed  securities are  short to
intermediate term  fixed  income  securities whose  values  at  maturity  (I.E.,
principal  value) and/or interest rates rise or  fall according to the change in
one  or  more  specified  underlying  instruments.  Indexed  securities  may  be
positively  or negatively indexed (I.E., their principal value or interest rates
may increase or decrease if the underlying instrument appreciates), and may have
return  characteristics  similar  to   direct  investments  in  the   underlying
instrument  or  to one  or more  options on  the underlying  instrument. Indexed
securities may be more volatile than the underlying instrument itself.
 
    SWAPS AND  RELATED TRANSACTIONS:  As one  way of  managing its  exposure  to
different  types of investments, the High  Income Series may enter into interest
rate swaps, currency swaps and other types of available swap agreements, such as
caps, collars and floors.  Swaps involve the exchange  by a Series with  another
party  of cash payments based upon  different interest rate indexes, currencies,
and other prices or rates, such as  the value of mortgage prepayment rates.  For
example,  in the typical interest rate swap,  a Series might exchange a sequence
of cash payments based  on a floating  rate index for cash  payments based on  a
fixed  rate. Payments made by both parties to  a swap transaction are based on a
principal amount determined by the parties.
 
    The High Income Series may also purchase and sell caps, floors and  collars.
In  a typical  cap or floor  agreement, one  party agrees to  make payments only
under specified circumstances,  usually in return  for payment of  a fee by  the
counterparty.  For example,  the purchase of  an interest rate  cap entitles the
buyer, to the  extent that a  specified index exceeds  a predetermined  interest
rate,  to receive payments of interest on a contractually-based principal amount
from the counterparty selling  such interest rate cap.  The sale of an  interest
rate  floor obligates the seller to make payments to the extent that a specified
interest rate falls below  an agreed-upon level.  A collar arrangement  combines
elements of buying a cap and selling a floor.
 
    Swap  agreements will tend  to shift a Series'  investment exposure from one
type of  investment to  another. For  example, if  a Series  agreed to  exchange
payments  in dollars for payments  in foreign currency, in  each case based on a
fixed rate, the swap agreement would tend to decrease a Series' exposure to U.S.
interest rates and increase its exposure to foreign currency and interest rates.
Caps and floors have an effect  similar to buying or writing options.  Depending
on  how they  are used,  swap agreements  may increase  or decrease  the overall
volatility of a Series' investments and its share price and yield.
 
    Swap agreements are sophisticated hedging instruments that typically involve
a small investment  of cash relative  to the  magnitude of risks  assumed. As  a
result,  swaps can be  highly volatile and  may have a  considerable impact on a
Series' performance.  Swap  agreements  are  subject to  risks  related  to  the
counterparty's   ability  to   perform,  and  may   decline  in   value  if  the
counterparty's creditworthiness deteriorates. A Series may also suffer losses if
it is unable  to terminate outstanding  swap agreements or  reduce its  exposure
through offsetting transactions.
 
                                       13
<PAGE>
    Swaps,  caps,  floors and  collars are  highly specialized  activities which
involve certain risks.  See the SAI  for further information  on, and the  risks
involved in, these activities.
 
    OPTIONS  ON SECURITIES: Each of the Series  may write (sell) covered put and
call options and  purchase put  and call options  on securities.  Each of  these
Series will write options on securities for the purpose of increasing its return
and/or  to protect  the value  of its portfolio.  In particular,  where a Series
writes an option that expires  unexercised or is closed out  by the Series at  a
profit,  it will retain the premium paid  for the option which will increase its
gross income and will offset in part the reduced value of the portfolio security
underlying the  option, or  the increased  cost of  portfolio securities  to  be
acquired.  In contrast, however,  if the price of  the underlying security moves
adversely to the Series'  position, the option may  be exercised and the  Series
will   be  required   to  purchase  or   sell  the  underlying   security  at  a
disadvantageous price, which may only be  partially offset by the amount of  the
premium.  The Series may also write combinations  of put and call options on the
same security, known as "straddles."  Such transactions can generate  additional
premium income but also present increased risk.
 
    By  writing a call option on a  security, a Series limits its opportunity to
profit from any increase in the  market value of the underlying security,  since
the  holder will usually exercise  the call option when  the market value of the
underlying security exceeds the exercise price of the call. However, the  Series
retains  the risk of depreciation in value of securities on which it has written
call options.
 
    Each of these Series may also  purchase put or call options in  anticipation
of  market fluctuations which may adversely affect the value of its portfolio or
the prices of securities that a Series wants to purchase at a later date. In the
event that the  expected market fluctuations  occur, the Series  may be able  to
offset  the resulting  adverse effect  on its  portfolio, in  whole or  in part,
through the options purchased. The  premium paid for a  put or call option  plus
any  transaction costs will reduce  the benefit, if any,  realized by the Series
upon exercise  or  liquidation of  the  option, and,  unless  the price  of  the
underlying security changes sufficiently, the option may expire without value to
the Series.
 
    In  certain instances, the Emerging Growth  Series may enter into options on
Treasury securities that  are "reset"  options or  "adjustable strike"  options.
These  options provide for periodic adjustment of  the strike price and may also
provide for  the periodic  adjustment of  the  premium during  the term  of  the
option. The SAI contains a further discussion of these investments.
 
    OPTIONS  ON STOCK INDICES: Each of the Emerging Growth Series and the Growth
With Income Series may  write (sell) covered call  and put options and  purchase
call and put options on stock indices. Each of these Series may write options on
stock  indices for the purpose of increasing its gross income and to protect its
portfolio against declines in  the value of securities  it owns or increases  in
the  value of  securities to be  acquired. When a  Series writes an  option on a
stock index,  and  the  value of  the  index  moves adversely  to  the  holder's
position, the option will not be exercised, and the Series will either close out
the  option at a profit or allow it to expire unexercised. A Series will thereby
retain the amount  of the premium,  less related transaction  costs, which  will
increase  its gross  income and  offset part of  the reduced  value of portfolio
securities  or  the  increased   cost  of  securities   to  be  acquired.   Such
transactions, however, will constitute only partial hedges against adverse price
fluctuations,  since any such fluctuations will be  offset only to the extent of
the premium received by  a Series for  the writing of  the option, less  related
transaction  costs.  In addition,  if  the value  of  an underlying  index moves
adversely to a  Series' option position,  the option may  be exercised, and  the
Series  will experience a loss which may  only be partially offset by the amount
of the premium received.
 
    Each of these Series may also purchase put or call options on stock  indices
in  order, respectively, to hedge its investments  against a decline in value or
to attempt to reduce the risk of missing a market or industry segment advance. A
Series' possible loss in either case will be limited to the premium paid for the
option, plus related transaction costs.
 
    "YIELD CURVE" OPTIONS: The High Income Series may enter into options on  the
yield  "spread," or  yield differential,  between two  securities, a transaction
referred to as a "yield curve" option, for hedging and non-hedging (an effort to
increase current income)  purposes. In  contrast to  other types  of options,  a
yield  curve option is based on the  difference between the yields of designated
securities rather than the  actual prices of the  individual securities, and  is
settled  through cash payments. Accordingly, a  yield curve option is profitable
to the holder if this differential widens (in the case of a call) or narrows (in
the case  of  a  put),  regardless  of whether  the  yields  of  the  underlying
securities increase or decrease. Yield curve options written by a Series will be
covered  as described in the SAI. The  trading of yield curve options is subject
to all
 
                                       14
<PAGE>
the risks associated  with trading other  types of options,  as discussed  below
under  "Additional  Risk Factors"  and  in the  SAI.  In addition,  such options
present risks of  loss even if  the yield  on one of  the underlying  securities
remains  constant, if the spread moves in a  direction or to an extent which was
not anticipated.
 
    FUTURES CONTRACTS AND OPTIONS ON  FUTURES CONTRACTS: The High Income  Series
may  purchase and  sell futures  contracts on  foreign or  domestic fixed income
securities or indices of such  securities, including municipal bond indices  and
any other indices of foreign or domestic fixed income securities that may become
available  for trading ("Futures  Contracts"). The Series  may also purchase and
write options on such Futures  Contracts ("Options on Futures Contracts").  Each
of the Emerging Growth Series and the Growth With Income Series may purchase and
sell  Futures Contracts on stock indices. Each of these Series may also purchase
and  sell  Futures  Contracts  on  foreign  currencies  or  indices  of  foreign
currencies.  Each of these  Series may also  purchase and write  Options on such
Futures Contracts.
 
    Such  transactions  will  be  entered  into  for  hedging  purposes  or  for
non-hedging purposes to the extent permitted by applicable law. Each Series will
incur  brokerage fees when it purchases and sells Futures Contracts, and will be
required to  maintain margin  deposits. In  addition, Futures  Contracts  entail
risks.  Although the Adviser believes that use  of such Contracts will benefit a
Series, if its investment judgment about the general direction of exchange rates
or the stock market is incorrect, the Series' overall performance may be  poorer
than  if it had not entered into any  such contract and the Series may realize a
loss. A  Series  will  not  enter  into  any  Futures  Contract  if  immediately
thereafter  the value  of securities and  other obligations  underlying all such
Futures Contracts held by such Series would exceed 50% of the value of its total
assets.
 
    Purchases of Options on Futures Contracts may present less risk in hedging a
Series' portfolio than the purchase or sale of the underlying Futures  Contracts
since  the potential loss is  limited to the amount  of the premium plus related
transaction costs,  although it  may  be necessary  to  exercise the  option  to
realize  any profit, which  results in the establishment  of a futures position.
The writing of Options on Futures Contracts, however, does not present less risk
than the trading of Futures Contracts and will constitute only a partial  hedge,
up  to  the  amount  of the  premium  received.  In addition,  if  an  option is
exercised, a Series may suffer a loss on the transaction.
 
    Futures Contracts and Options on Futures Contracts that are entered into  by
a Series will be traded on U.S. and foreign exchanges.
 
    FORWARD  CONTRACTS:  Each  of  the Series  may  enter  into  forward foreign
currency exchange contracts for the  purchase or sale of  a fixed quantity of  a
foreign  currency at a  future date ("Forward Contracts").  Each of these Series
may enter into Forward Contracts for  hedging purposes and (except for the  High
Income  Series)  for  non-hedging  purposes  (I.E.,  speculative  purposes).  By
entering into transactions in Forward  Contracts for hedging purposes, a  Series
may be required to forego the benefits of advantageous changes in exchange rates
and,  in the case of Forward Contracts  entered into for non-hedging purposes, a
Series may sustain losses which will reduce its gross income. Such transactions,
therefore,  could  be  considered  speculative.  Forward  Contracts  are  traded
over-the-counter  and not on organized commodities or securities exchanges. As a
result, Forward  Contracts operate  in a  manner distinct  from  exchange-traded
instruments,  and their use involves certain  risks beyond those associated with
transactions in Futures Contracts or options  traded on exchanges. A Series  may
choose  to,  or  be required  to,  receive  delivery of  the  foreign currencies
underlying Forward Contracts it has  entered into. Under certain  circumstances,
such  as  where  the  Adviser  believes that  the  applicable  exchange  rate is
unfavorable at the time the currencies are received or the Adviser  anticipates,
for  any other reason, that the exchange  rate will improve, the Series may hold
such currencies for an indefinite period of time. A Series may also enter into a
Forward Contract on  one currency  to hedge against  risk of  loss arising  from
fluctuations  in the value of a second currency (referred to as a "cross hedge")
if, in the judgment of  the Adviser, a reasonable  degree of correlation can  be
expected  between movements in the  values of the two  currencies. Each of these
Series has established procedures consistent with statements of the SEC and  its
staff regarding the use of Forward Contracts by registered investment companies,
which  requires  use of  segregated  assets or  "cover"  in connection  with the
purchase and sale of such contracts.
 
    OPTIONS ON FOREIGN  CURRENCIES: Each of  the Series may  purchase and  write
options  on foreign currencies ("Options on Foreign Currencies") for the purpose
of protecting against declines in the  dollar value of portfolio securities  and
against  increases in the  dollar cost of  securities to be  acquired. As in the
case of other types  of options, however,  the writing of  an Option on  Foreign
Currency  will constitute only a partial hedge,  up to the amount of the premium
received, and a Series
 
                                       15
<PAGE>
may be  required  to purchase  or  sell foreign  currencies  at  disadvantageous
exchange  rates, thereby incurring losses. The  purchase of an Option on Foreign
Currency may  constitute an  effective hedge  against fluctuations  in  exchange
rates although, in the event of rate movements adverse to a Series' position, it
may  forfeit the entire amount  of the premium paid  for the option plus related
transaction costs.  A Series  may also  choose to,  or be  required to,  receive
delivery  of the foreign currencies underlying  Options on Foreign Currencies it
has entered  into.  Under  certain  circumstances, such  as  where  the  Adviser
believes  that  the applicable  exchange  rate is  unfavorable  at the  time the
currencies are received or the Adviser  anticipates, for any other reason,  that
the  exchange  rate will  improve,  a Series  may  hold such  currencies  for an
indefinite period of time.
 
6.  ADDITIONAL RISK FACTORS
 
    OPTIONS, FUTURES CONTRACTS  AND FORWARD CONTRACTS:  Although certain  Series
will  enter into transactions in options,  Futures Contracts, Options on Futures
Contracts, Forward  Contracts  and Options  on  Foreign Currencies  for  hedging
purposes,  such transactions nevertheless involve  certain risks. For example, a
lack of  correlation between  the  instrument underlying  an option  or  Futures
Contract  and the  assets being hedged,  or unexpected  adverse price movements,
could render a Series' hedging strategy unsuccessful and could result in losses.
Certain Series also may enter  into transactions in options, Futures  Contracts,
Options  on  Futures  Contracts and  Forward  Contracts for  other  than hedging
purposes, which  involves greater  risk. In  particular, such  transactions  may
result  in losses for a Series which are  not offset by gains on other portfolio
positions, thereby reducing gross income. In addition, foreign currency  markets
may be extremely volatile from time to time. There also can be no assurance that
a  liquid secondary market will exist for  any contract purchased or sold, and a
Series may be  required to  maintain a  position until  exercise or  expiration,
which  could result in losses. The SAI  contains a description of the nature and
trading mechanics of options, Futures  Contracts, Options on Futures  Contracts,
Forward  Contracts and Options on Foreign  Currencies, and includes a discussion
of the risks related to transactions therein.
 
    Transactions  in  Forward  Contracts  may  be  entered  into  only  in   the
over-the-counter  market. Futures Contracts and Options on Futures Contracts may
be entered into  on U.S. exchanges  regulated by the  Commodity Futures  Trading
Commission  and on  foreign exchanges. In  addition, the  securities and indexes
underlying options, Futures Contracts and Options on Futures Contracts traded by
the Series will include both domestic and foreign securities.
 
    LOWER RATED BONDS: Each  of the Emerging Growth  Series and the High  Income
Series  may invest in fixed income securities rated Baa by Moody's or BBB by S&P
or Fitch and  comparable unrated  securities. These  securities, while  normally
exhibiting  adequate protection parameters, have speculative characteristics and
changes in economic conditions or other circumstances are more likely to lead to
a weakened capacity to make principal and interest payments than in the case  of
higher grade securities.
 
    Each  of these  Series may also  invest in  securities rated Ba  or lower by
Moody's or  BB  or lower  by  S&P or  Fitch  and comparable  unrated  securities
(commonly  known as "junk bonds") to the  extent described above. See Appendix A
to this Prospectus  for a  description of  these ratings.  These securities  are
considered  speculative  and,  while  generally  providing  greater  income than
investments in higher rated securities,  will involve greater risk of  principal
and income (including the possibility of default or bankruptcy of the issuers of
such  securities) and may involve greater volatility of price (especially during
periods of economic uncertainty or change) than securities in the higher  rating
categories.  However, since yields  vary over time, no  specific level of income
can ever be  assured. These lower  rated high yielding  fixed income  securities
generally tend to reflect economic changes and short-term corporate and industry
developments  to  a  greater extent  than  higher rated  securities  which react
primarily to fluctuations in the general level of interest rates (although these
lower rated fixed  income securities are  also affected by  changes in  interest
rates,  the market's  perception of  their credit  quality, and  the outlook for
economic growth). In  the past, economic  downturns or an  increase in  interest
rates have, under certain circumstances, caused a higher incidence of default by
the  issuers of these securities and may do  so in the future, especially in the
case of highly leveraged issuers. During certain periods, the higher yields on a
Series' lower rated  high yielding  fixed income securities  are paid  primarily
because of the increased risk of loss of principal and income, arising from such
factors as the heightened possibility of default or bankruptcy of the issuers of
such  securities. Due to the fixed income payments of these securities, a Series
may continue to earn the same level of interest income while its net asset value
declines due  to portfolio  losses, which  could result  in an  increase in  the
Series'  yield despite the actual loss of  principal. The market for these lower
rated fixed income securities may be less liquid than the market for  investment
grade
 
                                       16
<PAGE>
fixed  income  securities, and  judgment may  at  times play  a greater  role in
valuing these  securities than  in the  case of  investment grade  fixed  income
securities.  Changes in the value of  securities subsequent to their acquisition
will not  affect cash  income or  yield  to maturity  to a  Series but  will  be
reflected  in the net asset value of shares  of the Series. See the SAI for more
information on lower rated securities.
 
    FOREIGN SECURITIES: Each of the Series may invest in dollar-denominated  and
non-dollar-denominated  foreign securities.  Investing in  securities of foreign
issuers generally involves  risks not  ordinarily associated  with investing  in
securities  of  domestic  issuers.  These  include  changes  in  currency rates,
exchange  control  regulations,  governmental  administration  or  economic   or
monetary  policy (in  the U.S. or  abroad) or circumstances  in dealings between
nations. Costs may be  incurred in connection  with conversions between  various
currencies.  Special considerations  may also  include more  limited information
about foreign issuers,  higher brokerage costs,  different accounting  standards
and thinner trading markets. Foreign securities markets may also be less liquid,
more  volatile and  less subject  to government  supervision than  in the United
States. Investments  in foreign  countries could  be affected  by other  factors
including  expropriation,  confiscatory taxation  and potential  difficulties in
enforcing contractual obligations  and could be  subject to extended  settlement
periods.  All of the  Series (except the  Limited Maturity Series  and the Money
Market Series) may hold foreign currency received in connection with investments
in foreign  securities  when,  in the  judgment  of  the Adviser,  it  would  be
beneficial  to convert such currency into U.S. dollars at a later date, based on
anticipated changes in  the relevant exchange  rate. Such Series  may also  hold
foreign  currency in anticipation of purchasing  foreign securities. See the SAI
for further  discussion  of  foreign  securities  and  the  holding  of  foreign
currency, as well as the associated risks.
 
    AMERICAN  DEPOSITARY RECEIPTS: Each  of the Series may  invest in ADRs which
are certificates issued by  a U.S. depository (usually  a bank) and represent  a
specified  quantity of shares of an underlying  non-U.S. stock on deposit with a
custodian bank as collateral. Because  ADRs trade on U.S. securities  exchanges,
the Adviser does not treat them as foreign securities. However, they are subject
to many of the risks of foreign securities such as changes in exchange rates and
more limited information about foreign issuers.
 
    EMERGING  MARKET  SECURITIES:  Each of  the  Series may  invest  in emerging
markets. In addition to  the general risks of  investing in foreign  securities,
investments  in  emerging  markets  involve special  risks.  Securities  of many
issuers in emerging markets may be less liquid and more volatile than securities
of comparable domestic issuers. These  securities may be considered  speculative
and,  while  generally  offering higher  income  and the  potential  for capital
appreciation, may present significantly greater risk. Emerging markets may  have
different clearance and settlement procedures, and in certain markets there have
been  times when settlements  have been unable  to keep pace  with the volume of
securities transactions,  making  it  difficult to  conduct  such  transactions.
Delays  in settlement could  result in temporary  periods when a  portion of the
assets of a Series is uninvested and no return is earned thereon. The  inability
of a Series to make intended security purchases due to settlement problems could
cause a Series to miss attractive investment opportunities. Inability to dispose
of  portfolio securities due to settlement problems  could result in losses to a
Series due  to subsequent  declines  in value  of  the portfolio  securities,  a
decrease  in the level of  liquidity in a Series' portfolio,  or if a Series has
entered into  a  contract  to  sell the  security,  possible  liability  to  the
purchaser.  Certain markets may require  payment for securities before delivery,
and in such  markets a Series  bears the risk  that the securities  will not  be
delivered  and that the Series' payments will not be returned. Securities prices
in emerging  markets  can  be  significantly more  volatile  than  in  the  more
developed  nations  of  the  world,  reflecting  the  greater  uncertainties  of
investing in less  established markets and  economies. In particular,  countries
with emerging markets may have relatively unstable governments, present the risk
of   nationalization  of  businesses,  restrictions  on  foreign  ownership,  or
prohibitions of repatriation of assets, and may have less protection of property
rights than more developed countries.  The economies of countries with  emerging
markets  may be  predominantly based  on only  a few  industries, may  be highly
vulnerable to changes in local or  global trade conditions, and may suffer  from
extreme  and volatile debt burdens or  inflation rates. Local securities markets
may trade a small number of securities and may be unable to respond  effectively
to  increases  in  trading  volume,  potentially  making  prompt  liquidation of
substantial holdings difficult  or impossible  at times.  Securities of  issuers
located  in countries with  emerging markets may  have limited marketability and
may be subject to more abrupt or erratic movements.
 
    Certain  emerging  markets  may   require  governmental  approval  for   the
repatriation  of  investment  income,  capital  or  the  proceeds  of  sales  of
securities by foreign investors.  In addition, if a  deterioration occurs in  an
emerging market's
 
                                       17
<PAGE>
balance  of  payments or  for other  reasons, a  country could  impose temporary
restrictions on  foreign  capital  remittances.  A  Series  could  be  adversely
affected by delays in, or a refusal to grant, any required governmental approval
for  repatriation of capital, as well as by the application to the Series of any
restrictions on investments.
 
    Investment in  certain  foreign  emerging market  debt  obligations  may  be
restricted  or controlled to varying degrees. These restrictions or controls may
at times preclude investment in certain foreign emerging market debt obligations
and increase the expenses of a Series.
                              -------------------
 
SHORT-TERM INVESTMENTS FOR  TEMPORARY DEFENSIVE  PURPOSES --  During periods  of
unusual market conditions when the Adviser believes that investing for temporary
defensive  purposes is appropriate,  or in order  to meet anticipated redemption
requests, a large portion or all of the assets of each Series may be invested in
cash (including foreign currency) or cash equivalents including, but not limited
to,  obligations  of   banks  (including  certificates   of  deposit,   bankers'
acceptances,   time  deposits  and  repurchase  agreements),  commercial  paper,
short-term notes, U.S. Government Securities and related repurchase agreements.
 
PORTFOLIO TRADING
 
    Each  Series  intends  to  manage  its  portfolio  by  buying  and   selling
securities,  as  well as  holding  securities to  maturity,  to help  attain its
investment objectives and policies.
 
    Each Series will engage in portfolio  trading if it believes a  transaction,
net  of  costs  (including  custodian  charges),  will  help  in  attaining  its
investment objectives. In trading portfolio  securities, a Series seeks to  take
advantage  of  market  developments,  yield disparities  and  variations  in the
creditworthiness of issuers. For  a description of the  strategies which may  be
used  by the Series in trading portfolio securities, see "Portfolio Transactions
and Brokerage Commissions" in the SAI.
 
    Because the High Income Series is expected to have a portfolio turnover rate
of over 100%, transaction costs incurred by the Series and the realized  capital
gains  and losses of the Series may be greater than that of a fund with a lesser
portfolio turnover rate.
 
    The primary consideration  in placing portfolio  security transactions  with
broker-dealers  for execution  is to obtain,  and maintain  the availability of,
execution at  the  most  favorable  prices and  in  the  most  effective  manner
possible. Consistent with the foregoing primary consideration, the Rules of Fair
Practice  of the National  Association of Securities  Dealers, Inc. (the "NASD")
and such other policies as the Trustees of the Trust may determine, the  Adviser
may  consider sales of  Contracts for which  the Trust is  an investment option,
together with sales of  shares of other investment  company clients of MFS  Fund
Distributors, Inc., the distributor of shares of the Trust and of the MFS Family
of Funds, as a factor in the selection of broker-dealers to execute each Series'
portfolio  transactions.  From  time  to time  the  Adviser  may  direct certain
portfolio transactions to broker-dealer firms which, in turn, have agreed to pay
a portion of the Series' operating expenses (e.g., fees charged by the custodian
of the Series' assets). For a  further discussion of portfolio trading, see  the
SAI.
                              -------------------
 
    The  SAI includes a  discussion of other investment  policies and listing of
specific investment restrictions  which govern the  investment policies of  each
Series.  The specific investment  restrictions listed in the  SAI may be changed
without shareholder  approval  unless indicated  otherwise  (see the  SAI).  The
Series'  investment limitations, policies and rating standards are adhered to at
the  time  of  purchase  or  utilization  of  assets;  a  subsequent  change  in
circumstances will not be considered to result in a violation of policy.
 
7.  MANAGEMENT OF THE SERIES
 
    The   Trust's  Board  of  Trustees,  as   part  of  its  overall  management
responsibility, oversees  various  organizations responsible  for  each  Series'
day-to-day management.
 
INVESTMENT ADVISER -- MFS manages each Series pursuant to an Investment Advisory
Agreement  with the  Trust on behalf  of each  Series dated April  14, 1994 (the
"Advisory Agreement"). Under  the Advisory  Agreement, MFS  provides the  Series
 
                                       18
<PAGE>
with  overall  investment advisory  services. Subject  to  such policies  as the
Trustees may determine, MFS makes investment decisions for each Series. For  its
services  and  facilities,  MFS receives  a  management fee,  computed  and paid
monthly, in an amount equal to the  following annual rates of the average  daily
net assets of each Series:
 
<TABLE>
<CAPTION>
                                                                                              PERCENTAGE OF THE
                                                                                              AVERAGE DAILY NET
                                                                                                    ASSETS
SERIES                                                                                          OF EACH SERIES
- ------------------------------------------------------------------------------------------  ----------------------
<S>                                                                                         <C>
Emerging Growth Series....................................................................             0.75%
Growth With Income Series.................................................................             0.75%
High Income Series........................................................................             0.75%
</TABLE>
 
    For  the fiscal  year ended  December 31,  1996, MFS  received the following
management fees from  the Series under  the Advisory Agreement  and assumed  the
following amounts of the Series' expenses (see "Expenses" below);
 
<TABLE>
<CAPTION>
                                                                                 MANAGEMENT FEE  EXPENSES ASSUMED
SERIES                                                                            PAID TO MFS         BY MFS
- -------------------------------------------------------------------------------  --------------  ----------------
<S>                                                                              <C>             <C>
Emerging Growth Series.........................................................    $  314,262       $   62,962
Growth With Income Series......................................................        30,792           42,658
High Income Series.............................................................        56,169           45,293
</TABLE>
 
    MFS or its affiliates will pay a fee to Union Central Life Insurance Company
equal,  on an  annualized basis, to  0.10% of  the aggregate net  assets of each
Series, attributable to Contracts offered by separate accounts of Union  Central
Life  Insurance Company  or its affiliates.  Such fees  will not be  paid by the
Series, their shareholders, or by the Contract holders.
 
    The identity and background of the portfolio managers for each Series is set
forth below. Unless  indicated otherwise,  each portfolio manager  has acted  in
that capacity since the commencement of investment operations of each Series.
 
<TABLE>
<CAPTION>
SERIES                                                         PORTFOLIO MANAGERS
- -----------------------------  -----------------------------------------------------------------------------------
<S>                            <C>
Emerging Growth Series         John W. Ballen, a Senior Vice President of MFS, has been employed by the Adviser as
                               a  portfolio manager since 1984. Toni Y. Shimura, a Vice President of MFS, has been
                               employed by the Adviser  as a portfolio  manager since 1987.  Ms. Shimura became  a
                               portfolio manager of the Series on November 30, 1995.
Growth With Income Series      Kevin R. Parke, a Senior Vice President of MFS, has been employed by the Adviser as
                               a portfolio manager since 1985. John D. Laupheimer, a Senior Vice President of MFS,
                               has been employed by the Adviser as a portfolio manager since 1981.
High Income Series             Joan  S. Batchelder, a Senior  Vice President of the  Adviser, has been employed by
                               the Adviser as a portfolio manager since 1984.
</TABLE>
 
    MFS also serves as investment adviser to each of the other funds in the  MFS
Family  of Funds  (the "MFS Funds")  and to  MFS-Registered Trademark- Municipal
Income Trust, MFS Multimarket Income Trust, MFS Government Markets Income Trust,
MFS Intermediate  Income Trust,  MFS  Charter Income  Trust, MFS  Special  Value
Trust,  MFS Institutional Trust,  MFS Union Standard  Trust, MFS/Sun Life Series
Trust, and seven  variable accounts, each  of which is  a registered  investment
company established by Sun Life Assurance Company of Canada (U.S.) ("Sun Life of
Canada  (U.S.)") in connection  with the sale  of various fixed/variable annuity
contracts. MFS  and its  wholly owned  subsidiary, MFS  Institutional  Advisers,
Inc., provide investment advice to substantial private clients.
 
    MFS  is America's oldest  mutual fund organization.  MFS and its predecessor
organizations have  a history  of  money management  dating  from 1924  and  the
founding  of the first mutual fund in the United States, Massachusetts Investors
Trust.  Net  assets  under   the  management  of   the  MFS  organization   were
approximately  $52.8  billion on  behalf of  approximately 2.3  million investor
accounts as of February 28, 1997. As of such date, the MFS organization  managed
approximately  $28.9  billion  of  assets  invested  in  equity  securities  and
approximately $19.9  billion  of assets  invested  in fixed  income  securities.
Approximately  $4.0  billion  of  the  assets managed  by  MFS  are  invested in
securities of foreign issuers and non-U.S. dollar-denominated securities of U.S.
issuers. MFS is a subsidiary  of Sun Life of Canada  (U.S.), which in turn is  a
wholly  owned subsidiary of  Sun Life Assurance Company  of Canada ("Sun Life").
The Directors of MFS are A. Keith  Brodkin, Jeffrey L. Shames, Arnold D.  Scott,
John D. McNeil and Donald A. Stewart. Mr. Brodkin is the Chairman, Mr. Shames is
the  President  and Mr.  Scott  is the  Secretary  and a  Senior  Executive Vice
President of MFS.
 
                                       19
<PAGE>
Messrs. McNeil and Stewart are the Chairman and President, respectively, of  Sun
Life.  Sun  Life,  a  mutual  life insurance  company,  is  one  of  the largest
international life  insurance companies  and has  been operating  in the  United
States  since  1895,  establishing  a  headquarters  office  here  in  1973. The
executive officers of MFS report to the Chairman of Sun Life.
 
    A. Keith Brodkin, the Chairman  and a Director of  MFS, is the Chairman  and
President  and a Trustee of the Trust. W. Thomas London, Stephen E. Cavan, James
R. Bordewick, Jr.,  and James  O. Yost,  all of whom  are officers  of MFS,  are
officers of the Trust.
 
    MFS  has established a strategic alliance with Foreign & Colonial Management
Ltd. ("Foreign & Colonial"). Foreign  & Colonial is a  subsidiary of two of  the
world's  oldest  financial  services institutions,  the  London-based  Foreign &
Colonial Investment Trust PLC, which pioneered the idea of investment management
in 1868, and HYPO-BANK (Bayerische Hypotheken-und Weschsel-Bank AG), the  oldest
publicly  listed bank in Germany, founded in 1835. As part of this alliance, the
portfolio managers and investment analysts of  MFS and Foreign & Colonial  share
their  views on  a variety  of investment related  issues, such  as the economy,
securities  markets,  portfolio   securities  and   their  issuers,   investment
recommendations,  strategies and  techniques, risk  analysis, trading strategies
and other  portfolio  management  matters.  MFS  has  access  to  the  extensive
international  equity investment expertise of Foreign  & Colonial, and Foreign &
Colonial has access to  the extensive U.S. equity  investment expertise of  MFS.
MFS  and Foreign Colonial each have investment personnel working in each other's
offices in Boston and London, respectively.
 
    In certain  instances there  may  be securities  which  are suitable  for  a
Series'  portfolio as well as for portfolios  of other clients of MFS or clients
of Foreign  &  Colonial.  Some simultaneous  transactions  are  inevitable  when
several  clients  receive investment  advice from  MFS  and Foreign  & Colonial,
particularly when the same security is suitable for more than one client.  While
in  some cases this arrangement could have  a detrimental effect on the price or
availability of the security as  far as a Series  is concerned, in other  cases,
however, it may produce increased investment opportunities for the Series.
 
    From  time to time, the Adviser may  purchase, redeem and exchange shares of
any Series. The  purchase by  the Adviser  of shares of  a Series  may have  the
effect  of  lowering that  Series' expense  ratio, while  the redemption  by the
Adviser of shares of  a Series may  have the effect  of increasing that  Series'
expense ratio.
 
    DISTRIBUTOR   --  MFS  Fund  Distributors,  Inc.  ("MFD"),  a  wholly  owned
subsidiary of MFS, is the distributor of  shares of each Series and also  serves
as distributor for certain of the other mutual funds managed by MFS.
 
    ADMINISTRATOR  --  MFS  provides  the  Series  with  certain  administrative
services pursuant to a Master  Administrative Services Agreement dated March  1,
1997.  Under this  Agreement, MFS  provides the  Series with  certain financial,
legal, compliance, shareholder communications and other administrative services.
As a partial reimbursement for the cost of providing these services, the  Series
pays  MFS an administrative  fee up to  0.015% per annum  of the Series' average
daily net assets,  provided that  the administrative fee  is not  assessed on  a
Series' assets that exceed $3 billion.
 
    SHAREHOLDER  SERVICING AGENT --  MFS Service Center,  Inc. (the "Shareholder
Servicing Agent"), a wholly owned  subsidiary of MFS, performs transfer  agency,
certain dividend disbursing agency and other services for each Series.
 
8.  INFORMATION CONCERNING SHARES OF EACH SERIES
 
PURCHASES AND REDEMPTIONS
 
    The  separate accounts of the Participating Insurance Companies place orders
to purchase and redeem shares of each  Series based on, among other things,  the
amount of premium payments to be invested and surrender and transfer requests to
be  effected on that day pursuant to Contracts. Orders received by the Trust are
effected on days on which the Exchange is open for trading. For orders  received
by  the Trust before  the close of  regular trading on  the Exchange (normally 4
p.m. eastern time), such purchases and redemptions of the shares of each  Series
are  effected at the respective net asset  values per share determined as of the
close of  regular  trading on  the  Exchange  on that  same  day.  Participating
Insurance  Companies shall be the designee of  the Trust for receipt of purchase
and redemption orders from Contract holders  and receipt by such designee  shall
constitute receipt by the Trust; provided that the Trust receives notice of such
order  by 9:30 a.m. eastern time on the next following day on which the Exchange
is open for trading. Payment for shares shall be by federal funds transmitted by
wire and must be received by 2:00 p.m. eastern time on the next following day on
which the Exchange  is open for  trading after the  purchase order is  received.
Redemption proceeds shall be by
 
                                       20
<PAGE>
federal funds transmitted by wire and shall be sent by 2:00 p.m. eastern time on
the  next following  day on  which the  Exchange is  open for  trading after the
redemption order  is received.  No fee  is charged  the shareholders  when  they
redeem Series shares.
 
    The  offering of shares of any Series may  be suspended for a period of time
and each  Series reserves  the  right to  refuse  any specific  purchase  order.
Purchase  orders may be refused if, in the Adviser's opinion, they are of a size
that would disrupt the management of a  Series. The Trust may suspend the  right
of  redemption of shares of any Series  and may postpone payment for any period:
(i) during which the Exchange is closed other than customary weekend and holiday
closings or during which  trading on the Exchange  is restricted; (ii) when  the
SEC  determines  that a  state of  emergency  exists which  may make  payment or
transfer not reasonably practicable;  (iii) as the SEC  may by order permit  for
the  protection of the security  holders of the Trust; or  (iv) at any time when
the Trust may, under applicable laws, rules and regulations, suspend payment  on
the redemption of its shares.
 
    Should  any conflict between Contract holders arise which would require that
a substantial  amount  of net  assets  be  withdrawn from  any  Series,  orderly
portfolio  management  could be  disrupted to  the  potential detriment  of such
Contract.
 
NET ASSET VALUE
 
    The net asset value per share of  each Series is determined each day  during
which  the Exchange is open for trading.  This determination is made once during
each such day as of  the close of regular trading  on the Exchange by  deducting
the  amount of the Series' liabilities from  the value of the Series' assets and
dividing the  difference by  the number  of shares  of the  Series  outstanding.
Values  of assets in  a Series' portfolio  are determined on  the basis of their
market or other fair value (amortized cost value in the case of the Money Market
Series), as described in  the SAI. All investments,  assets and liabilities  are
expressed in U.S. dollars based upon current currency exchange rates.
 
DISTRIBUTIONS
 
    Substantially  all of  each Series' net  investment income  for any calendar
year is declared as dividends  and paid to its  shareholders as dividends on  an
annual basis. In addition, each Series may make one or more distributions during
the  calendar year to its shareholders from any long-term capital gains, and may
also make one or more distributions to its shareholders from short-term  capital
gains.  In determining the  net investment income  available for distribution, a
Series may rely on projections of  its anticipated net investment income  (which
may  include  short-term capital  gains from  the sales  of securities  or other
assets, and,  if allowed  by a  Series' investment  restrictions, premiums  from
options  written), over  a longer  term, rather  than its  actual net investment
income for the period.
 
    Shareholders of any of the Series may elect to receive dividends and capital
gain distributions in either cash or additional shares.
 
TAX STATUS
 
    Each Series of the Trust is treated as a separate entity for federal  income
tax  purposes. In  order to  minimize the taxes  each Series  would otherwise be
required to  pay, each  Series intends  to  qualify each  year as  a  "regulated
investment  company" under Subchapter M of the Internal Revenue Code of 1986, as
amended ("the Code"). Because each Series  intends to distribute all of its  net
investment  income and net capital gains  to its shareholders in accordance with
the timing requirements imposed by the Code, it is not expected that any of  the
Series will be required to pay entity level federal income or excise taxes.
 
    Shares  of  the  Series  are offered  only  to  the  Participating Insurance
Companies' separate accounts  that fund Contracts.  See the applicable  Contract
prospectus  for a  discussion of  the federal  income tax  treatment of  (1) the
separate accounts that purchase  and hold Series shares  and (2) the holders  of
the  Contracts  that  are funded  through  those  accounts. In  addition  to the
diversification requirements  of Subchapter  M  of the  Code, each  Series  also
intends  to diversify its assets as required  by Code Section 817(h)(1), and the
regulations thereunder. See also "Tax Status" in the SAI.
 
DESCRIPTION OF SHARES, VOTING RIGHTS AND LIABILITIES
 
    Each Series currently has one class of shares, entitled Shares of Beneficial
Interest (without par  value). The Trust  has reserved the  right to create  and
issue  additional classes  and series  of shares,  in which  case each  class of
shares of a  series would  participate equally  in the  earnings, dividends  and
assets  attributable to that  class of that  particular series. Shareholders are
entitled to one vote for each share held, and shares of each Series are entitled
to vote separately to
 
                                       21
<PAGE>
approve investment  advisory agreements  or changes  in investment  restrictions
with  respect to  that Series,  but shares  of all  Series vote  together in the
election of Trustees  and selection  of accountants.  Additionally, each  Series
will  vote separately on any  other matter that affects  solely that Series, but
will otherwise vote  together with all  other Series on  all other matters.  The
Trust  does not intend  to hold annual shareholder  meetings. The Declaration of
Trust provides that a Trustee may  be removed from office in certain  instances.
See "Description of Shares, Voting Rights and Liabilities" in the SAI.
 
    Each  share of  a Series represents  an equal proportionate  interest in the
Series with each  share, subject to  the liabilities of  the particular  Series.
Shares  have no pre-emptive or conversion rights. Shares are fully paid and non-
assessable. Should a Series  be liquidated, shareholders  are entitled to  share
PRO  RATA in the  net assets available for  distribution to shareholders. Shares
will remain on  deposit with  the Shareholder Servicing  Agent and  certificates
will not be issued.
 
    The  Trust  is an  entity of  the  type commonly  known as  a "Massachusetts
business trust."  Under Massachusetts  law, shareholders  of such  a trust  may,
under  certain  circumstances, be  held personally  liable  as partners  for its
obligations. However,  the risk  of a  shareholder incurring  financial loss  on
account  of  shareholder liability  is limited  to  circumstances in  which both
inadequate insurance existed (E.G., fidelity bonding and omission insurance) and
the Trust itself was unable to meet its obligations.
 
    United of Omaha Life Insurance Company,  Omaha, NE, owns 75.63% of the  High
Income  Series' shares, and,  therefore, controls the  Series; and Union Central
Life  Insurance  Company--Group  Annuity   and  Union  Central  Life   Insurance
Company--Individual   Annuity,   Cincinnati,   OH,   own   28.17%   and  52.03%,
respectively, of the  Growth With  Income Series' shares,  and, therefore,  each
controls the Series.
 
PERFORMANCE INFORMATION
 
    Each Series' performance may be quoted in advertising in terms of yield and,
except  for  the Money  Market  Series, total  return.  Performance is  based on
historical  results  and  is  not  intended  to  indicate  future   performance.
Performance  quoted for a  Series includes the effect  of deducting that Series'
expenses,  but  may  not  include  charges  and  expenses  attributable  to  any
particular  insurance  product. Excluding  these  charges from  quotations  of a
Series' performance  has  the  effect  of  increasing  the  performance  quoted.
Performance  for a  Series will  vary based on,  among other  things, changes in
market conditions, the  level of  interest rates and  the level  of the  Series'
expenses.  For further information about the  Series' performance for the fiscal
year ended December 31, 1996, please see  the Series' Annual Reports. A copy  of
these   Annual  Reports  may  be  obtained  without  charge  by  contacting  the
Shareholder Servicing Agent (see back cover for address and phone number).
 
    From time to time,  quotations of a  Series' total return  and yield may  be
included  in  advertisements, sales  literature  or reports  to  shareholders or
prospective investors. The total return of a Series refers to return assuming an
investment has been  held in the  Series for one  year and for  the life of  the
Series  (the ending date of  which will be stated).  The total return quotations
may be expressed in terms  of average annual or  cumulative rates of return  for
all  periods quoted.  Average annual total  return refers to  the average annual
compound rate of return  of an investment in  a Series. Cumulative total  return
represents  the cumulative change  in value of  an investment in  a Series. Both
will assume that all dividends and capital gains distributions were  reinvested.
The yield of a Series refers to net investment income generated by a Series over
a specified 30-day (or one month) period. This income is then "annualized." That
is,  the amount  of income generated  by the  Series during that  30-day (or one
month) period is assumed to be generated over a 12-month period and is shown  as
a percentage of net asset value.
 
EXPENSES
 
    The  Trust pays the compensation of the Trustees who are not officers of MFS
and all expenses of each Series (other than those assumed by MFS) including  but
not  limited to: governmental fees; interest  charges; taxes; membership dues in
the Investment Company Institute allocable to each Series; fees and expenses  of
independent  auditors, of legal counsel, and of any transfer agent, registrar or
dividend disbursing agent of each Series; expenses of repurchasing and redeeming
shares and servicing shareholder accounts;  expenses of preparing, printing  and
mailing   prospectuses,  periodic  reports,  notices  and  proxy  statements  to
shareholders and to governmental officers  and commissions; brokerage and  other
expenses  connected with  the execution,  recording and  settlement of portfolio
security transactions; insurance premiums;
 
                                       22
<PAGE>
fees and expenses of Investors Bank & Trust Company, the Trust's Custodian,  for
all  services to each Series, including  safekeeping of funds and securities and
maintaining required books and accounts;  expenses of calculating the net  asset
value  of shares of each Series;  and expenses of shareholder meetings. Expenses
relating to  the issuance,  registration  and qualification  of shares  of  each
Series  and the preparation,  printing and mailing of  prospectuses are borne by
each Series except that the Distribution Agreement with MFD requires MFD to  pay
for  prospectuses that are to be used  for sales purposes. Expenses of the Trust
which are not attributable to a specific Series are allocated between the Series
in a manner believed by management of the Trust to be fair and equitable.
 
    Subject to termination or  revision at the sole  discretion of MFS, MFS  has
agreed  to bear expenses of each of  the Series such that the respective Series'
"Other Expenses," which are defined to include all expenses of the Series except
for management fees, do not exceed 0.25% of the average daily net assets of  the
Series  (the "Maximum Percentage"). The obligation of MFS to bear these expenses
for a Series terminates on the last day of the Series' fiscal year in which  its
"Other  Expenses" are less than or equal to the Maximum Percentage. The payments
made by MFS  on behalf  of each  Series under  this arrangement  are subject  to
reimbursement by the Series to MFS, which will be accomplished by the payment of
an expense reimbursement fee by the Series to MFS computed and paid monthly at a
percentage  of the Series' average daily net  assets for its then current fiscal
year, with a limitation that immediately  after such payment the Series'  "Other
Expenses"  will not exceed the Maximum Percentage. This expense reimbursement by
each Series to MFS terminates on the earlier of the date on which payments  made
by  the Series equal the  prior payment of such  reimbursable expenses by MFS or
December 31, 2004.
 
SHAREHOLDER COMMUNICATIONS
 
    Owners of Contracts  issued by Participating  Insurance Companies for  which
shares  of one or more  Series are the investment  vehicle will receive from the
Participating Insurance Companies semi-annual  financial statements and  audited
year-end  financial statements  certified by  the Trust's  independent certified
public accountants. Each report will show the investments owned by the Trust and
the valuations thereof  as determined  by the  Trustees and  will provide  other
information about the Trust and its operations.
 
    Participating  Insurance Companies  with inquiries  regarding the  Trust may
call the Trust's Shareholder  Servicing Agent. (See back  cover for address  and
phone number.)
                              -------------------
 
    The  SAI for the Trust,  dated May 1, 1997,  as amended or supplemented from
time to  time, contains  more detailed  information about  each of  the  Series,
including  information related to: (i)  the investment policies and restrictions
of each Series; (ii) the Trustees, officers and investment adviser of the Trust;
(iii) portfolio transactions; (iv) the  shares of each Series, including  rights
and  liabilities of  shareholders; (v)  the method  used to  calculate yield and
total rate of return  quotations of each Series;  (vi) the determination of  net
asset  value  of shares  of  each Series;  and  (vii) certain  voting  rights of
shareholders of each Series.
 
                                       23
<PAGE>
                                                                      APPENDIX A
 
                          DESCRIPTION OF BOND RATINGS
 
The ratings of Moody's, S&P and Fitch represent their opinions as to the quality
of  various debt instruments. It should be emphasized, however, that ratings are
not absolute standards of quality. Consequently, debt instruments with the  same
maturity,  coupon and rating may have different yields while debt instruments of
the same maturity and coupon with different ratings may have the same yield.
 
                        MOODY'S INVESTORS SERVICE, INC.
 
    AAA: Bonds which are rated  Aaa are judged to be  of the best quality.  They
carry  the smallest degree of  investment risk and are  generally referred to as
"gilt edged." Interest payments are protected by a large or by an  exceptionally
stable margin and principal is secure. While the various protective elements are
likely  to change, such changes as can be visualized are most unlikely to impair
the fundamentally strong position of such issues.
 
    AA: Bonds  which are  rated Aa  are  judged to  be of  high quality  by  all
standards. Together with the Aaa group they comprise what are generally known as
high  grade bonds. They are  rated lower than the  best bonds because margins of
protection may  not  be  as  large  as in  Aaa  securities  or  fluctuations  of
protective  elements may be of greater amplitude  or there may be other elements
present which  make the  long-term  risks appear  somewhat  larger than  in  Aaa
securities.
 
    A:  Bonds which are rated A possess many favorable investment attributes and
are to be considered as upper-medium-grade obligations. Factors giving  security
to  principal and interest are considered  adequate, but elements may be present
which suggest a susceptibility to impairment sometime in the future.
 
    BAA: Bonds which are  rated Baa are  considered as medium-grade  obligations
(I.E.,  they are neither highly protected nor poorly secured). Interest payments
and principal security appear  adequate for the  present but certain  protective
elements  may be lacking or may  be characteristically unreliable over any great
length of time. Such  bonds lack outstanding  investment characteristics and  in
fact have speculative characteristics as well.
 
    BA:  Bonds which are rated Ba are judged to have speculative elements; their
future cannot be considered  as well-assured. Often  the protection of  interest
and  principal payments  may be very  moderate and thereby  not well safeguarded
during both  good  and  bad  times over  the  future.  Uncertainty  of  position
characterizes bonds in this class.
 
    B:  Bonds which are rated B  generally lack characteristics of the desirable
investment. Assurance of interest  and principal payments  or of maintenance  of
other terms of the contract over any long period of time may be small.
 
    CAA:  Bonds which are rated Caa are of  poor standing. Such issues may be in
default or there may be present elements of danger with respect to principal  or
interest.
 
    CA:  Bonds which are rated Ca represent obligations which are speculative in
a  high  degree.  Such  issues  are  often  in  default  or  have  other  marked
shortcomings.
 
    C: Bonds which are rated C are the lowest rated class of bonds and issues so
rated  can be regarded as having extremely  poor prospects of ever attaining any
real investment standing.
 
    ABSENCE OF RATING: Where no rating has  been assigned or where a rating  has
been  suspended or withdrawn, it may be  for reasons unrelated to the quality of
the issue.
 
    Should no rating be assigned, the reason may be one of the following:
 
    1.  an application for rating was not received or accepted;
 
    2.  the issue or issuer belongs  to a group of securities or companies  that
       are not rated as a matter of policy;
 
    3.  there is a lack of essential data pertaining to the issue or issuer; or
 
    4.    the  issue was  privately  placed, in  which  case the  rating  is not
       published in Moody's publications.
 
                                      A-1
<PAGE>
    Suspension or withdrawal may occur if new and material circumstances  arise,
the  effects  of which  preclude satisfactory  analysis; if  there is  no longer
available reasonable up-to-date  data to permit  a judgment to  be formed; if  a
bond is called for redemption; or for other reasons.
 
                       STANDARD & POOR'S RATINGS SERVICES
 
    AAA:  Debt rated AAA has the highest rating assigned by S&P. Capacity to pay
interest and repay principal is extremely strong.
 
    AA: Debt rated  AA has  a very  strong capacity  to pay  interest and  repay
principal and differs from the highest rated issues only in small degree.
 
    A:  Debt rated A has a strong  capacity to pay interest and repay principal,
although it is somewhat  more susceptible to the  adverse effects of changes  in
circumstances and economic conditions than debt in higher-rated categories.
 
    BBB:  Debt  rated BBB  is regarded  as  having an  adequate capacity  to pay
interest and repay principal. Whereas  it normally exhibits adequate  protection
parameters,  adverse  economic  conditions or  changing  circumstances  are more
likely to lead to a  weakened capacity to pay  interest and repay principal  for
debt in this category than in higher-rated categories.
 
    BB:  Debt rated  BB has less  near-term vulnerability to  default than other
speculative issues. However, it faces major ongoing uncertainties or exposure to
adverse  business,  financial,  or  economic  conditions  which  could  lead  to
inadequate  capacity  to meet  timely interest  and  principal payments.  The BB
rating category  is also  used for  debt  subordinated to  senior debt  that  is
assigned an actual or implied BBB- rating.
 
    B: Debt rated B has a greater vulnerability to default but currently has the
capacity  to meet interest payments  and principal repayments. Adverse business,
financial or economic conditions will  likely impair capacity or willingness  to
pay  interest and repay principal.  The B rating category  is also used for debt
subordinated to senior  debt that is  assigned an  actual or implied  BB or  BB-
rating.
 
    CCC:  Debt rated CCC has a  currently identifiable vulnerability to default,
and is dependent upon favorable  business, financial and economic conditions  to
meet  timely payment  of interest  and repayment of  principal. In  the event of
adverse business, financial, or  economic conditions, it is  not likely to  have
the  capacity to pay  interest and repay  principal. The CCC  rating category is
also used for debt  subordinated to senior  debt that is  assigned an actual  or
implied B or B- rating.
 
    CC:  The rating CC is typically applied  to debt subordinated to senior debt
that is assigned an actual or implied CCC rating.
 
    C: The rating  C is typically  applied to debt  subordinated to senior  debt
which  is assigned an  actual or implied CCC-  debt rating. The  C rating may be
used to cover a situation where a  bankruptcy petition has been filed, but  debt
service payments are continued.
 
    CI: The rating CI is reserved for income bonds on which no interest is being
paid.
 
    D:  Debt rated D is  in payment default. The D  rating category is used when
interest payments or principal payments  are not made on  the date due, even  if
the  applicable  grace period  has not  expired, unless  S&P believes  that such
payments will be made during such grace  period. The D rating also will be  used
upon  the  filing  of  a  bankruptcy  petition  if  debt  service  payments  are
jeopardized.
 
    PLUS (+) OR MINUS  (-): The ratings from  AA to CCC may  be modified by  the
addition  of a  plus or minus  sign to  show relative standing  within the major
rating categories.
 
    NR: Indicates  that no  public  rating has  been  requested, that  there  is
insufficient  information on which to base a rating, or that S&P does not rate a
particular type of obligation as a matter of policy.
 
                                      A-2
<PAGE>
A-1 AND P-1 COMMERCIAL PAPER RATINGS
 
Description of S&P, Fitch and Moody's highest commercial paper ratings:
 
    The rating "A" is  the highest commercial paper  rating assigned by S&P  and
Fitch,  and issues  so rated  are regarded as  having the  greatest capacity for
timely payment. Issues in the "A" category are delineated with the numbers 1,  2
and  3 to indicate the relative degree  of safety. The A-1 designation indicates
that the degree  of safety regarding  timely payment is  either overwhelming  or
very  strong.  Those  A-1  issues  determined  to  possess  overwhelming  safety
characteristics will be denoted with a plus (+) sign designation.
 
    The rating P-1 is the highest  commercial paper rating assigned by  Moody's.
Issuers  rated P-1 have a superior ability for repayment. P-1 repayment capacity
will normally be evidenced by the following characteristics: (1) leading  market
positions  in well  established industries;  (2) high  rates of  return on funds
employed; (3) conservative  capitalization structure with  moderate reliance  on
debt and ample asset protection; (4) broad margins in earnings coverage of fixed
financial  charges and high  internal cash generation;  and (5) well established
access to  a  range  of  financial markets  and  assured  sources  of  alternate
liquidity.
 
                         FITCH INVESTORS SERVICE, INC.
 
    AAA:  Bonds  considered to  be investment  grade and  of the  highest credit
quality. The obligor  has an exceptionally  strong ability to  pay interest  and
prepay  principal, which  is unlikely to  be affected  by reasonably foreseeable
events.
 
    AA: Bonds considered to be investment grade and of very high credit quality.
The obligor's  ability to  pay  interest and  repay  principal is  very  strong,
although  not quite as strong  as bonds rated 'AAA'.  Because bonds rated in the
'AAA' and 'AA' categories are not significantly vulnerable to foreseeable future
developments, short-term debt of these issuers is generally rated 'F-1+'.
 
    A: Bonds considered to be investment grade and of very high credit  quality.
The  obligor's ability to pay  interest and repay principal  is considered to be
strong, but may be more vulnerable to adverse changes in economic conditions and
circumstances than bonds with higher ratings.
 
    BBB: Bonds  considered to  be investment  grade and  of satisfactory  credit
quality. The obligor's ability to pay interest and repay principal is considered
to  be  adequate.  Adverse  changes in  economic  conditions  and circumstances,
however, are more likely to have  adverse impact on these bonds and,  therefore,
impair  timely payment. The likelihood that the ratings of these bonds will fall
below investment grade is higher than for bonds with higher ratings.
 
    BB: Bonds are considered speculative. The obligor's ability to pay  interest
and  repay  principal may  be affected  over time  by adverse  economic changes.
However, business  and  financial alternatives  can  be identified  which  could
assist the obligor in satisfying its debt service requirements.
 
    B:  Bonds are considered  highly speculative. While bonds  in this class are
currently meeting debt service requirements, the probability of continued timely
payment of  principal and  interest  reflects the  obligor's limited  margin  of
safety and the need for reasonable business and economic activity throughout the
life of the issue.
 
    CCC: Bonds have certain identifiable characteristics which, if not remedied,
may  lead to default.  The ability to meet  obligations requires an advantageous
business and economic environment.
 
    CC: Bonds are  minimally protected.  Default in payment  of interest  and/or
principal seems probable over time.
 
    C: Bonds are in imminent default in payment of interest of principal.
 
    PLUS(+)  MINUS(-): Plus  and minus  signs are used  with a  rating symbol to
indicate the relative position of a  credit within the rated category. Plus  and
minus signs, however, are not used in the 'AAA' category.
 
    NR: indicates that Fitch does not rate the specific issue.
 
    CONDITIONAL:  A conditional rating is  premised on the successful completion
of a project or the occurrence of a specific event.
 
                                      A-3
<PAGE>
    SUSPENDED: A rating is suspended when Fitch deems the amount of  information
available from the issuer to be inadequate for rating purposes.
 
    WITHDRAWN:  A rating will be withdrawn when an issue matures or is called or
refinanced, and, at Fitch's discretion, when  an issuer fails to furnish  proper
and timely information.
 
    FITCHALERT:  Ratings  are placed  on FitchAlert  to  notify investors  of an
occurrence that is likely to result in a rating change and the likely  direction
of  such  change.  These are  designated  a "Positive,"  indicating  a potential
upgrade, "Negative," for potential downgrade,  or "Evolving," where ratings  may
be lowered. FitchAlert is relatively short-term and should be resolved within 12
months.
 
                                      A-4
<PAGE>
                                                                      APPENDIX B
 
                             MFS HIGH INCOME SERIES
                          PORTFOLIO COMPOSITION CHART
                    FOR FISCAL YEAR ENDED DECEMBER 31, 1996
 
The table below shows the percentages of the Series' assets at December 31, 1996
invested  in bonds  assigned to  the various  rating categories  by S&P, Moody's
(provided only for bonds not rated by  S&P), Fitch (provided only for bonds  not
rated by S&P or Moody's) and Duff & Phelps (provided only for bonds not rated by
S&P,  Moody's  or  Fitch)  and in  unrated  bonds  determined by  MFS  to  be of
comparable quality. For split rated bonds, the  S&P rating is used. When an  S&P
rating  is unavailable, secondary  sources are selected  in the following order:
Moody's, Fitch and Duff & Phelps.
 
<TABLE>
<CAPTION>
                         UNRATED BONDS
             COMPILED    OF COMPARABLE
RATING        RATINGS       QUALITY        TOTAL
- ----------  -----------  --------------  ----------
<S>         <C>          <C>             <C>
AAA/Aaa
AA/Aa
A/A
BBB/Baa
BB/Ba            12.02                       12.02
B/B              69.41          3.93         73.34
CCC/Caa           4.49                        4.49
CC/Ca
C/C
Default            .58                         .58
                 -----         -----         -----
    TOTAL        86.50          3.93         90.43
</TABLE>
 
The chart does  not necessarily  indicate what  the composition  of the  Series'
portfolio will be in subsequent years. Rather, the Series' investment objective,
policies  and restrictions indicate the extent  to which the Series may purchase
securities in the various categories.
 
                                      B-1
<PAGE>
INVESTMENT ADVISER
Massachusetts Financial Services Company
500 Boylston Street, Boston, MA 02116
(617) 954-5000
(800) 637-8730
 
DISTRIBUTOR
MFS Fund Distributors, Inc.
500 Boylston Street, Boston, MA 02116
(617) 954-5000
CUSTODIAN
Investors Bank & Trust Company
89 South Street, Boston, MA 02111
 
DIVIDEND DISBURSING AGENT
State Street Bank and Trust Company
225 Franklin Street, Boston, MA 02110
 
SHAREHOLDER SERVICING AGENT
MFS Service Center, Inc.
500 Boylston Street, Boston, MA 02116
Toll free: (800) 343-2829, ext. 3500
MAILING ADDRESS:
P.O. Box 1400, Boston, MA 02104-9985
INDEPENDENT AUDITORS
Deloitte & Touche LLP
125 Summer Street, Boston, MA 02110
 
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                       MFS-REGISTERED TRADEMARK- EMERGING
                                 GROWTH SERIES
                     MFS-REGISTERED TRADEMARK- GROWTH WITH
                                 INCOME SERIES
                     MFS-REGISTERED TRADEMARK- HIGH INCOME
                                     SERIES
 
                                     [LOGO]
 
                                   PROSPECTUS
 
                                  MAY 1, 1997
 
                                     [LOGO]
 
                MFS-REGISTERED TRADEMARK- EMERGING GROWTH SERIES
              MFS-REGISTERED TRADEMARK- GROWTH WITH INCOME SERIES
                  MFS-REGISTERED TRADEMARK- HIGH INCOME SERIES
                     500 Boylston Street, Boston, MA 02116
 
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