MFS VARIABLE INSURANCE TRUST
497, 1998-08-20
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MFS[RegTM] EMERGING GROWTH SERIES
MFS[RegTM] RESEARCH SERIES
MFS[RegTM] GROWTH WITH INCOME SERIES                        PROSPECTUS
MFS[RegTM] NEW DISCOVERY SERIES                             May 1, 1998
- --------------------------------------------------------------------------------
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 13
separate mutual fund series (individually or collectively hereinafter referred
to as a "Series" or the "Series"), four 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 Research Series (the "Research Series"), which seeks to provide long-term
   growth of capital and future income;
- -- 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 New Discovery Series (the "New Discovery Series"), which seeks capital
   appreciation.
                                ----------------

  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.
                                ----------------
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, 1998, as amended or supplemented from time to time ("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 (http://www.sec.gov) 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.
                                ----------------
SHARES OF THE TRUST ARE AVAILABLE AND ARE BEING MARKETED AS A POOLED FUNDING
VEHICLE FOR LIFE INSURANCE COMPANIES WRITING ALL TYPES OF CONTRACTS.
                                ----------------
THE EMERGING GROWTH SERIES, THE RESEARCH SERIES, THE GROWTH WITH INCOME SERIES
AND THE NEW DISCOVERY SERIES ARE INTENDED FOR INVESTORS WHO UNDERSTAND AND ARE
WILLING TO ACCEPT THE RISKS ENTAILED IN SEEKING LONG-TERM GROWTH OF CAPITAL OR
CAPITAL APPRECIATION. 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.

    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. Condensed Financial Information ...............................     4
 3. Investment Concept of the Trust ...............................     7
 4. Investment Objectives and Policies ............................     7
         MFS Emerging Growth Series ...............................     8
         MFS Research Series ......................................     8
         MFS Growth With Income Series ............................     9
         MFS New Discovery Series .................................     9
 5. Certain Securities and Investment Techniques ..................    10
 6. Additional Risk Factors .......................................    16
 7. Management of the Series ......................................    19
 8. Information Concerning Shares of Each Series ..................    20
         Purchases and Redemptions ................................    20
         Net Asset Value ..........................................    21
         Distributions ............................................    22
         Tax Status ...............................................    22
         Description of Shares, Voting Rights and Liabilities .....    22
         Performance Information ..................................    23
         Expenses .................................................    23
         Shareholder Communications ...............................    24
Appendix A--Description of Bond Ratings ...........................   A-1
</TABLE>

                                        2


<PAGE>


1. EXPENSE SUMMARY

Annual Operating Expenses (as a percentage of average net assets):

<TABLE>
<CAPTION>
                                                                           MFS
                                                                         Emerging             MFS
                                                                          Growth            Research
                                                                          Series             Series
                                                                         --------           --------
    <S>                                                                    <C>                <C>
    Management Fee ..............................................          0.75%              0.75%
    Other Expenses (after expense limitation)(1) ................          0.12%              0.13%
                                                                           ----               ----
    Total Operating Expenses (after expense limitation) .........          0.87%              0.88%

                                                                           MFS                MFS
                                                                          Growth              New
                                                                        With Income        Discovery
                                                                          Series             Series
                                                                        -----------        ---------
    Management Fee ..............................................          0.75%              0.90%
    Other Expenses (after expense limitation)(1) ................          0.25%(2)           0.25%(2)
                                                                           ----               ----
    Total Operating Expenses (after expense limitation) .........          1.00%(2)           1.15%(2)
</TABLE>

- --------------------
(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 these Series, subject to
    reimbursement by these Series, such that each such 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" and "Total Operating
    Expenses" for each such Series would be:

<TABLE>
<CAPTION>
                                             "Other Expenses"     "Total Operating Expenses"
                                              Without Expense          Without Expense
       Series                                   Limitation                Limitation
       ------                                ----------------     --------------------------
       <S>                                          <C>                      <C>
       Growth With Income ...............           0.35%                    1.10%
       New Discovery (estimate) .........           0.47%                    1.37%
</TABLE>

                               Example of Expenses

     An investor would pay the following dollar amounts of expenses on a $1,000
investment in each Series, assuming (a) 5% annual return and (b) redemption at
the end of each of the time periods indicated:

<TABLE>
<CAPTION>
                                                    Period
                                     -------------------------------------
       Series                        1 Year   3 Years   5 Years   10 Years
       ------                        ------   -------   -------   --------
<S>                                    <C>      <C>       <C>       <C>
       Emerging Growth ............    $ 9      $29       $ 50      $111
       Research ...................      9       29         51       113
       Growth With Income .........     10       32         55       122
       New Discovery ..............     12       37        N/A       N/A
</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.

     The "Example" set forth above should not be considered a representation of
past or future expenses of any Series; actual expenses may be greater or less
than those shown.

                                        3


<PAGE>


2. CONDENSED FINANCIAL INFORMATION

     The following financial information has been audited since the commencement
of investment operations of each 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            Year Ended           Period Ended
                                                             December 31, 1997     December 31, 1996     December 31, 1995*
                                                             -----------------     -----------------     ------------------
<S>                                                              <C>                   <C>                     <C>
Per share data (for a share outstanding throughout
 each period):
Net asset value--beginning of period ....................        $  13.24              $  11.41                $10.00
                                                                 --------              --------                ------
Income from investment operations#--
 Net investment income (loss)[sec] ......................        $  (0.06)             $  (0.01)               $ 0.01
 Net realized and unrealized gain on investments and
   foreign currency transactions ........................            2.95                  1.95                  1.74
                                                                 --------              --------                ------
   Total from investment operations .....................        $   2.89              $   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)                   --
 From capital ...........................................              --                    --                 (0.07)
                                                                 --------              --------                ------
   Total distributions declared to shareholders .........        $     --              $  (0.11)               $(0.34)
                                                                 --------              --------                ------
Net asset value--end of period ..........................        $  16.13              $  13.24                $11.41
                                                                 ========              ========                ======
Total return ............................................           21.90%                17.02%                17.41%++
Ratios (to average net assets)/Supplemental data[sec]:
 Expenses ...............................................            0.90%                 1.00%                 1.00%+
 Net investment income (loss) ...........................           (0.38)%               (0.08)%                0.10%+
Portfolio turnover ......................................             112%                   96%                   73%
Average commission rate### ..............................        $ 0.0616              $ 0.0401                    --
Net assets at end of period (000 omitted) ...............        $384,480              $104,956                $3,869
</TABLE>

- --------------------
    * For the period from the commencement of the Series' investment operations,
      July 24, 1995, through December 31, 1995.
    + Annualized.
   ++ Not annualized.
    # Per share data are based on average shares outstanding.
   ## The Series' expenses are calculated without reduction for fees paid
      indirectly.
  ### Average commission rate is calculated for Series' with fiscal years
      beginning on or after September 1, 1995.
[sec] The investment adviser voluntarily agreed to maintain, subject to
      reimbursement by the Series, the expenses of the Series at no more than
      1.00% of average daily net assets. To the extent actual expenses were over
      or under this limitation, the net investment loss per share and the ratios
      would have been:
<TABLE>
     <S>                                  <C>           <C>            <C>
     Net investment loss ...........      $(0.05)       $(0.03)        $(0.18)
     Ratios (to average net assets):
       Expenses## ..................        0.87%         1.16%          2.91%+
       Net investment loss .........       (0.35)%       (0.23)%        (1.78)%+
</TABLE>

                                        4


<PAGE>


                                 Research Series

<TABLE>
<CAPTION>
                                                                 Year Ended            Year Ended           Period Ended
                                                             December 31, 1997     December 31, 1996     December 31, 1995*
                                                             -----------------     -----------------     ------------------
<S>                                                              <C>                    <C>                    <C>
Per share data (for a share outstanding throughout
 each period):
Net asset value--beginning of period ....................        $  13.13               $ 10.89                $10.00
                                                                 --------               -------                ------
Income from investment operations#--
 Net investment income[sec] .............................        $   0.05               $  0.06                $ 0.05
 Net realized and unrealized gain on investments and
   foreign currency transactions ........................            2.62                  2.37                  1.01
                                                                 --------               -------                ------
   Total from investment operations .....................        $   2.67               $  2.43                $ 1.06
                                                                 --------               -------                ------
Less distributions declared to shareholders--
 From net investment income .............................        $     --               $ (0.02)               $(0.03)
 From net realized gain on investments and foreign
   currency transactions ................................              --                 (0.16)                (0.14)
 In excess of net realized gain on investments and
   foreign currency transactions ........................              --                 (0.01)                   --
                                                                 --------               -------                ------
   Total distributions declared to shareholders .........        $     --               $ (0.19)               $(0.17)
                                                                 --------               -------                ------
Net asset value--end of period ..........................        $  15.80               $ 13.13                $10.89
                                                                 ========               =======                ======
Total return ............................................           20.26%                22.33%                10.62%++
Ratios (to average net assets)/Supplemental data[sec]:
 Expenses ...............................................            0.92%                 1.00%                 1.00%+
 Net investment income ..................................            0.34%                 0.47%                 1.15%+
Portfolio turnover ......................................              99%                   56%                   28%
Average commission rate### ..............................        $ 0.0544               $0.0295                    --
Net assets at end of period (000 omitted) ...............        $285,845               $35,710                $2,530
</TABLE>

- --------------------
    * For the period from the commencement of the Series' investment operations,
      July 26, 1995, through December 31, 1995.
    + Annualized.
   ++ Not annualized.
    # Per share data are based on average shares outstanding.
   ## The Series' expenses are calculated without reduction for fees paid
      indirectly.
  ### Average commission rate is calculated with fiscal years beginning on or
      after September 1, 1995.
[sec] The investment adviser voluntarily agreed to maintain, subject to
      reimbursement by the Series, the expenses of the Series at not more than
      1.00% of average daily net assets. To the extent actual expenses were over
      or under this limitation, the net investment income (loss) per share and
      the ratios would have been:

<TABLE>
     <S>                                          <C>           <C>          <C>
     Net investment income (loss) ..........      $0.06           --         $(0.08)
     Ratios (to average net assets):
      Expenses## ...........................       0.88%        1.48%          3.90%+
      Net investment income (loss) .........       0.38%          --          (1.73)%+
</TABLE>

                                        5


<PAGE>


                            Growth With Income Series

<TABLE>
<CAPTION>
                                                                 Year Ended            Year Ended           Period Ended
                                                             December 31, 1997     December 31, 1996     December 31, 1995*
                                                             -----------------     -----------------     ------------------
<S>                                                               <C>                   <C>                    <C>
Per share data (for a share outstanding throughout
 each period):
Net asset value--beginning of period ....................         $ 12.98               $ 10.61                $10.00
                                                                  -------               -------                ------
Income from investment operations#--
 Net investment income[sec] .............................         $  0.16               $  0.18                $ 0.05
 Net realized and unrealized gain on investments and
   foreign currency transactions ........................            3.70                  2.42                  0.61
                                                                  -------               -------                ------
   Total from investment operations .....................         $  3.86               $  2.60                $ 0.66
                                                                  -------               -------                ------
Less distributions declared to shareholders--
 From net investment income .............................         $ (0.07)              $ (0.09)               $(0.05)
 From net realized gain on investments and foreign
   currency transactions ................................           (0.29)                (0.13)                   --
 In excess of net realized gain on investments and
   foreign currency transactions ........................           (0.04)                (0.01)                   --
                                                                  -------               -------                ------
   Total distributions declared to shareholders .........         $ (0.40)              $ (0.23)               $(0.05)
                                                                  -------               -------                ------
Net asset value--end of period ..........................         $ 16.44               $ 12.98                $10.61
                                                                  =======               =======                ======
Total return ............................................           29.78%                24.46%                 6.64%++
Ratios (to average net assets)/Supplemental data[sec]:
 Expenses ...............................................            1.00%                 1.00%                 1.00%+
 Net investment income ..................................            0.93%                 1.52%                 2.20%+
Portfolio turnover ......................................              42%                   41%                    2%
Average commission rate### ..............................         $0.0455               $0.0351                    --
Net assets at end of period (000 omitted) ...............         $58,045               $ 9,174                $  365
</TABLE>

- --------------------
    * For the period from the commencement of the Series' investment
      operations, October 9, 1995, through December 31, 1995.
    + Annualized.
   ++ Not annualized.
    # Per share data are based on average shares outstanding.
   ## For fiscal years ending after September 1, 1995, expenses are
      calculated without reduction for fees paid indirectly.
  ### Average commission rate is calculated for Series with fiscal years
      beginning on or after September 1, 1995.
[sec] 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 this limitation, the net investment income (loss) per
      share and the ratios would have been:
<TABLE>
     <S>                                          <C>          <C>           <C>
     Net investment income (loss) ..........      $0.13        $0.05         $ (0.41)
     Ratios (to average net assets):
      Expenses## ...........................       1.10%        2.07%          21.44%+
      Net investment income (loss) .........       0.82%        0.46%         (18.24)%+
</TABLE>

                                        6


<PAGE>


3. INVESTMENT CONCEPT OF THE TRUST

     The Trust is an open-end, registered management investment company
comprised of the following thirteen series: Emerging Growth Series, Value
Series, Research Series, Growth With Income Series, Total Return Series,
Utilities Series, High Income Series, World Governments Series, Emerging Markets
Equity Series, Bond Series, Limited Maturity Series, Money Market Series and New
Discovery Series. Each Series is a segregated, separately managed portfolio of
securities. All of the Series, except the Utilities Series and the World
Governments 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 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.

     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. 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 "Certain Securities and Investment Techniques" below and in the SAI
under the caption "Certain Securities and Investment Techniques." The Series'
investments are subject to certain risks, as

                                        7


<PAGE>


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"), Fitch
IBCA ("Fitch") or Duff & Phelps Credit Rating Co. ("Duff & Phelps")) (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 Research Series -- The Research Series' investment objective is to provide
long-term growth of capital and future income.

     The portfolio securities of the Research Series are selected by a committee
of investment research analysts. This committee includes investment analysts
employed not only by the Adviser but also by MFS International (U.K.) Limited, a
wholly owned subsidiary of MFS. The Series' assets are allocated among
industries by the analysts acting together as a group. Individual analysts are
then responsible for selecting what they view as the securities best suited to
meet the Series' investment objective within their assigned industry
responsibility.

     The Research Series' policy is to invest a substantial proportion of its
assets in equity securities of companies believed to possess better than average
prospects for long-term growth. A smaller proportion of the assets may be
invested in bonds, short-term obligations, preferred stocks or common stocks
whose principal characteristic is income production

                                        8


<PAGE>


rather than growth. Such securities may also offer opportunities for growth of
capital as well as income. In the case of both growth stocks and income issues,
emphasis is placed on the selection of progressive, well-managed companies. The
Series' non-convertible debt investments, if any, may consist of "investment
grade" securities (rated Baa or better by Moody's or BBB or better by S&P or by
Fitch), and, with respect to no more than 10% of the Series' net assets,
securities in the lower rated categories (rated Ba or lower by Moody's or BB or
lower by S&P, by Fitch or by Duff & Phelps) or securities which the Adviser
believes to be of similar quality to these lower rated securities (commonly
known as "junk bonds"). For a description of bond ratings, see Appendix A to
this Prospectus.

     Consistent with its investment objective and policies described above, the
Series may also invest up to 20% of its net assets in foreign securities
(including emerging market securities) 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.

     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 New Discovery Series -- The New Discovery Series' investment objective is to
seek capital appreciation.

     The Series seeks to achieve its objective by investing, under normal market
conditions, at least 65% of its total assets in companies that the Adviser
believes offer superior prospects for growth. Such securities may either be
listed on securities exchanges or traded in the over-the-counter markets and may
be U.S. or foreign companies. While companies in which the Series invests may be
of any size, such as companies in a relatively early stage of development that
offer the potential for accelerated earnings or revenue growth (emerging growth
companies), or larger or more established companies whose rates of earnings
growth are expected to accelerate because of special factors, such as
rejuvenated management, new products, or structural changes in the economy, the
Series will generally invest in companies with small market capitalizations
relative to companies included in the Standard & Poor's 500 Stock Index. 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, management and market opportunities which are usually
necessary to become more widely recognized as growth companies. The Series seeks
to maintain a portfolio weighted median capitalization of $2 billion or less.

     The Series may also invest in fixed income securities offering an
opportunity for capital appreciation, including up to 10% of its net assets in
fixed income securities rated BB or lower by S&P, Fitch or Duff & Phelps, or Ba
or lower by Moody's, or if unrated, determined to be of equivalent quality by
the Adviser (commonly referred to as "junk bonds"). For a description of these
ratings, see Appendix B to the Prospectus (see also "Additional Risk Factors -
Lower Rated Bonds" in the Prospectus.

     The Series may engage in short sales of securities which the Adviser
expects to decline in price (see "Short Sales" below).

     Consistent with its investment objective and policies described above, the
Series may also invest up to (but not including) 20% of its net assets in
foreign securities which are not traded on a U.S. exchange (not including
American Depositary Receipts).

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5. CERTAIN SECURITIES AND INVESTMENT TECHNIQUES

     Equity Securities: Each of the Series may invest in all types of equity
securities, including the following: common stocks, preferred stocks and
preference stocks; securities such as bonds, warrants or rights that are
convertible into stocks; and depository receipts for those securities. These
securities may be listed on securities exchanges, traded in various
over-the-counter markets or have no organized markets.

     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 of the 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 or Sub-Adviser, as applicable, 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 or Sub-Adviser, as applicable,
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
location of its 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 (except the Research 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, Croatia, Dominican Republic, Ecuador,
Jordan, Mexico, Morocco, Nigeria, Panama, Peru, the Philippines, Poland,
Slovenia, 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

                                       10


<PAGE>


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 (except the Research 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 segregate liquid assets sufficient to cover its commitments.

     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 of the liquidity determinations, 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: The Emerging Growth 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.

                                       11


<PAGE>


     Zero Coupon Bonds, Deferred Interest Bonds and PIK Bonds: Each of the
Growth With Income Series and the New Discovery Series may invest in zero coupon
bonds. Zero coupon 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. Zero coupon bonds do not require the
periodic payment of interest. 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.
Each 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.

     Loan Participations and Other Direct Indebtedness: The Emerging Growth
Series may invest a portion of its assets in "loan participations" and other
direct indebtedness. By purchasing a loan participation, the 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. The 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 the 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.

     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.

     Foreign Growth Securities: Each of the Series may invest in securities of
foreign growth companies, including established foreign 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 or which otherwise represent opportunities
for long-term growth. See "Risk Factors" below. It is anticipated that these
companies will primarily be in nations with more developed securities markets,
such as Japan, Australia, Canada, New Zealand and most Western European
countries, including Great Britain.

     Depositary Receipts: Each of the Series may invest in American Depositary
Receipts ("ADRs"). ADRs 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 generally 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. Generally, ADRs are in registered form and are designed for use in U.S.
securities markets.

     Indexed Securities: The New Discovery 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 changes
in the value of one or more specified underlying instruments. Indexed securities
may be positively

                                       12


<PAGE>


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 and could
involve the loss of all or a portion of the principal amount of or interest on
the instrument.

     Swaps and Related Transactions: As one way of managing its exposure to
different types of investments, the New Discovery 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
notional principal amount determined by the parties.

     Swap agreements could be used 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,
or no investment of cash. 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.

     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 Emerging Growth Series, the Growth With
Income Series and the New Discovery 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.
However, the writing of options constitutes only a partial hedge, up to the
amount of the premium, less any transaction costs. In contrast, 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

                                       13


<PAGE>


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, the Growth
With Income Series and the New Discovery 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 New Discovery 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 the Series will
be covered as described in the SAI. The trading of yield curve options is
subject to all 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 New Discovery
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, the Growth With Income Series,
and the New Discovery Series may purchase and sell Futures Contracts on stock
indices, and 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

                                       14


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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.

     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 Bond
Series and 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 or Sub-Adviser, as applicable,
believes that the applicable exchange rate is unfavorable at the time the
currencies are received or the Adviser or Sub-Adviser, as applicable,
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 or Sub-Adviser, as applicable,
a reasonable degree of correlation can be expected between movements in the
values of the two currencies. Each of these Series has established procedures
which require use of segregated assets or "cover" in connection with the
purchase and sale of such contracts.

     Options on Foreign Currencies: Each of the Emerging Growth Series, the
Growth With Income Series and the New Discovery 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 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.

     Short Sales: If the New Discovery Series anticipates that the price of a
security will decline, it may sell the security short and borrow the same type
of security from a broker or other institution to complete the sale. The Series
may make

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<PAGE>


a profit or loss depending upon whether the market price of the security
decreases or increases between the date of the short sale and the date on which
the Series must replace the borrowed security. Possible losses from short sales
differ from losses that could be incurred from a purchase of a security, because
losses from short sales may be unlimited, whereas losses from purchases of a
security can equal only the total amount invested. The Series will segregate
liquid assets to cover its short sale obligations. The Series will not sell
short securities whose underlying value, minus amounts pledged by the Series as
collateral (which does not include the proceeds from the short sale), exceeds
40% of its net assets.

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 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, the Research Series,
and the New Discovery Series may invest in fixed income securities rated Baa by
Moody's or BBB by S&P, Fitch or Duff & Phelps 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, Fitch or Duff & Phelps 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.

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<PAGE>


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 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: 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. Each of the 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.

     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 bal-

                                       17


<PAGE>


ance 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 or Sub-Adviser, as applicable,
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 of the 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 of the 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 Emerging Growth 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 New Discovery Series is not anticipated to
have a portfolio turnover rate in excess of 100%.

     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 Conduct Rules
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). Except
with respect to the Series' policy on borrowing and investing in illiquid
securities, 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.

                                       18


<PAGE>


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 Amended and
Restated Investment Advisory Agreement with the Trust on behalf of each Series
dated April 14, 1994, as amended and restated on April 30, 1998 (the "Advisory
Agreement"). Under the Advisory Agreement, MFS provides the Series 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%
Research Series ...................             0.75%
Growth With Income Series .........             0.75%
New Discovery Series ..............             0.90%
</TABLE>

     For the fiscal year ended December 31, 1997, 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 ............      $1,887,980           $     0
Research Series ...................       1,343,324                 0
Growth With Income Series .........         188,365            26,920
</TABLE>

     MFS or its affiliates will pay a fee to Midland National Life Insurance
Company ("Midland") equal, on an annualized basis, to 0.15% of the aggregate net
assets of the Trust attributable to Contracts offered by separate accounts of
Midland or their 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, an Executive 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.

Research Series               The Series is currently managed by a committee comprised of various equity research
                              analysts employed by the Adviser.

Growth With Income Series     Kevin R. Parke, an Executive 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.

New Discovery Series          Brian E. Stack, a Vice President of the Adviser, has been employed by the Adviser as a
                              portfolio manager since 1993.
</TABLE>

                                       19


<PAGE>


     MFS also serves as investment adviser to each of the other funds in the MFS
Family of Funds (the "MFS Funds") and to MFS[RegTM] 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/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.), a subsidiary of Sun Life Assurance Company
of Canada ("Sun Life"), in connection with the sale of various fixed/variable
annuity contracts. MFS and its wholly owned subsidiary, MFS Institutional
Advisors, 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 $72.0 billion on behalf of approximately 2.8 million investor
accounts as of January 30, 1998. As of such date, the MFS organization managed
approximately $47.2 billion of assets invested in equity securities and
approximately $20.8 billion of assets invested in fixed income securities.
Approximately $4.2 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.) Financial Services
Holdings, Inc., which in turn is an indirect wholly owned subsidiary of Sun
Life. The Directors of MFS are Jeffrey L. Shames, Arnold D. Scott, John W.
Ballen, John D. McNeil and Donald A. Stewart. Mr. Shames is the Chairman and
President and Mr. Scott is the Secretary and a Senior Executive Vice President
of MFS. Mr. Ballen is an Executive Vice President and Chief Equity Officer.
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.

     W. Thomas London, Stephen E. Cavan, James R. Bordewick, Jr., Ellen
Moynihan, Mark E. Bradley and James O. Yost, all of whom are officers of MFS,
are officers of the Trust.

     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 each of the other mutual funds managed by MFS.

Administrator -- MFS provides each Series with certain financial, legal,
compliance, shareholder communications and other administrative services
pursuant to a Master Administrative Services Agreement dated March 1, 1997, as
amended. Under this Agreement, each Series pays MFS an administrative fee of up
to 0.015% per annum of the Series' average daily net assets. This fee reimburses
MFS for a portion of the costs it incurs to provide such services.

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

                                       20


<PAGE>


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 generally 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 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.

     At the sole discretion of the Trust, each Series may pay redemptions either
totally or partially by a distribution in-kind of securities (instead of cash)
from such Series' portfolio. The securities distributed in such a distribution
would be valued at the same amount as that assigned to them in calculating the
net asset value for the shares being sold. Securities distributed by a Series
will be selected by the Adviser in light of the Series' objective and may not
generally represent a pro rata distribution of each security held in the Series'
portfolio. If a shareholder received a distribution in-kind, the shareholder
could incur brokerage or transaction charges when converting the securities to
cash.

     Purchases and exchanges should be made for investment purposes only. The
Trust and MFD each reserves the right to reject or restrict any specific
purchase or exchange request. The Trust is not designed for professional market
timing organizations or other entities using programmed or frequent exchanges.
The Trust defines a "market timer" as an individual, or organization acting on
behalf of one or more individuals, if the individual or organization makes six
or more exchange requests out of any Series per calendar year. Accounts under
common ownership or control, including accounts administered by market timers,
will be aggregated for purposes of this definition.

     As noted above, the Trust and MFD each reserves the right to reject or
restrict any specific purchase and exchange request and, in addition, may impose
specific limitations with respect to market timers, including delaying for up to
seven days the purchase side of an exchange request by market timers or
specifically rejecting or otherwise restricting purchase and exchange requests
by market timers. In the event that any individual or entity is determined
either by the Trust or MFD, in its sole discretion, to be a market timer with
respect to any calendar year, the Trust and/or MFD may reject all exchange
requests into the Series during the remainder of that year.

     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, as described in the SAI. All investments, assets and
liabilities are expressed in U.S. dollars based upon current currency exchange
rates.

                                       21


<PAGE>


Distributions

     All of each Series' net investment income for any calendar year is declared
and paid to its shareholders as dividends on an annual basis. In addition, each
Series will make one or more distributions during the calendar year to its
shareholders from any net realized long-term and short-term capital gains.

     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 RIC 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 realized 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 any 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 continue 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 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.

     As of February 27, 1998, Merrill Lynch Life Insurance Company,
Jacksonville, FL, owns of record 25.58% of the Emerging Growth Series' shares
and 42.18% of the Research Series' shares, and, therefore, is a controlling
entity of such Series.

                                       22


<PAGE>


Performance Information

     Each Series' performance may be quoted in advertising in terms of yield and
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, 1997, 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: advisory and administrative services; 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; fees and expenses of State Street Bank and 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 (after
taking into effect any compensating balance and offset arrangements) except for
management fees, taxes, extraordinary expenses, and brokerage and transaction
costs, do not exceed 0.25% of the average daily net assets of the Series (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. The obligation of MFS to bear a Series' Other Expenses pursuant to
this arrangement, and the Series' obligation to pay the reim-

                                       23


<PAGE>


bursement fee 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 (May 1, 2001, in the case of the New Discovery Series).

     The expense reimbursement arrangement has terminated for the Emerging
Growth Series and Research Series.

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, 1998, 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.

                                       24


<PAGE>


                                                                     APPENDIX A

                           Description of Bond Ratings

     The ratings of Moody's, S&P, Fitch and Duff & Phelps 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.

                                       A-1


<PAGE>


     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.

     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: An obligation rated `AAA' has the highest rating assigned by Standard
& Poor's. The obligor's capacity to meet its financial commitment on the
obligation is EXTREMELY STRONG.

     AA: An obligation rated `AA' differs from the highest rated obligations
only in small degree. The obligor's capacity to meet its financial commitment on
the obligation is VERY STRONG.

     A: An obligation rated `A' is somewhat more susceptible to the adverse
effects of changes in circumstances and economic conditions than obligations in
higher rated categories. However, the obligor's capacity to meet its financial
commitment on the obligation is still STRONG.

     BBB: An obligation rated `BBB' exhibits ADEQUATE protection parameters.
However, adverse economic conditions or changing circumstances are more likely
to lead to a weakened capacity of the obligor to meet its financial commitment
on the obligation.

     Obligations rated `BB', `B', `CCC', `CC', and `C' are regarded as having
significant speculative characteristics. `BB' indicates the least degree of
speculation and `C' the highest. While such obligations will likely have some
quality and protective characteristics, these may be outweighed by large
uncertainties or major exposures to adverse conditions.

     BB: An obligation rated `BB' is LESS VULNERABLE to nonpayment than other
speculative issues. However, it faces major ongoing uncertainties or exposure to
adverse business, financial, or economic conditions which could lead to the
obligor's inadequate capacity to meet its financial commitment on the
obligation.

     B: An obligation rated `B' is MORE VULNERABLE to nonpayment than
obligations rated `BB', but the obligor currently has the capacity to meet its
financial commitment on the obligation. Adverse business, financial, or economic
conditions will likely impair the obligor's capacity or willingness to meet its
financial commitment on the obligation.

     CCC: An obligation rated `CCC' is CURRENTLY VULNERABLE to nonpayment, and
is dependent upon favorable business, financial, and economic conditions for the
obligor to meet its financial commitment on the obligation. In the event of
adverse business, financial, or economic conditions, the obligor is not likely
to have the capacity to meet its financial commitment on the obligation.

     CC: An obligation rated `CC' is CURRENTLY HIGHLY VULNERABLE to nonpayment.

     C: The `C' rating may be used to cover a situation where a bankruptcy
petition has been filed or similar action has been taken, but payments on this
obligation are being continued.

                                       A-2


<PAGE>


     D: An obligation rated `D' is in payment default. The `D' rating category
is used when payments on an obligation are not made on the date due even if the
applicable grace period has not expired, unless Standard & Poor's 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 or the taking of a similar action
if payments on an obligation 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.

     r: This symbol is attached to the ratings of instruments with significant
noncredit risks. It highlights risks to principal or volatility of expected
returns which are not addressed in the credit rating. Examples include:
obligations linked or indexed to equities, currencies, or commodities;
obligations exposed to severe prepayment risk--such as interest-only or
principal-only mortgage securities; and obligations with unusually risky
interest terms, such as inverse floaters.

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 IBCA

     AAA: Highest credit quality. `AAA' ratings denote the lowest expectation of
credit risk. They are assigned only in case of exceptionally strong capacity for
timely payment of financial commitments. This capacity is highly unlikely to be
adversely affected by foreseeable events.

     AA: Very high credit quality. `AA' ratings denote a very low expectation of
credit risk. They indicate very strong capacity for timely payment of financial
commitments. This capacity is not significantly vulnerable to foreseeable
events.

     A: High credit quality. `A' ratings denote a low expectation of credit
risk. The capacity for timely payment of financial commitments is considered
strong. This capacity may, nevertheless, be more vulnerable to changes in
circumstances or in economic conditions than is the case for higher ratings.

     BBB: Good credit quality. `BBB' ratings indicate that there is currently a
low expectation of credit risk. The capacity for timely payment of financial
commitments is considered adequate, but adverse changes in circumstances and in
economic conditions are more likely to impair this capacity. This is the lowest
investment-grade category.

Speculative Grade

     BB: Speculative. `BB' ratings indicate that there is a possibility of
credit risk developing, particularly as the result of adverse economic change
over time; however, business or financial alternatives may be available to allow
financial commitments to be met. Securities rated in this category are not
investment grade.

                                       A-3


<PAGE>


     B: Highly speculative. `B' ratings indicate that significant credit risk is
present, but a limited margin of safety remains. Financial commitments are
currently being met; however, capacity for continued payment is contingent upon
a sustained, favorable business and economic environment.

     CCC, CC, C: High default risk. Default is a real possibility. Capacity for
meeting financial commitments is solely reliant upon sustained, favorable
business or economic developments. A `CC' rating indicates that default of some
kind appears probable. `C' ratings signal imminent default.

     DDD, DD, and D: Default. Securities are not meeting current obligations and
are extremely speculative. `DDD' designates the highest potential for recovery
of amounts outstanding on any securities involved. For U.S. corporates, for
example, `DD' indicates expected recovery of 50%-90% of such outstandings, and
`D' the lowest recovery potential, i.e. below 50%.

                         Duff & Phelps Credit Rating Co.

     AAA: Highest credit quality. The risk factors are negligible, being only
slightly more than for risk-free U.S. Treasury debt.

     AA+, AA, AA-: High credit quality. Protection factors are strong. Risk is
modest but may vary slightly from time to time because of economic conditions.

     A+, A, A-: Protection factors are average but adequate. However, risk
factors are more variable and greater in periods of economic stress.

     BBB+, BBB, BBB-: Below-average protection factors but still considered
sufficient for prudent investment. Considerable variability in risk during
economic cycles.

     BB+, BB, BB-: Below investment grade but deemed likely to meet obligations
when due. Present or prospective financial protection factors fluctuate
according to industry conditions or company fortunes. Overall quality may move
up or down frequently within this category.

     B+, B, B-: Below investment grade and possession risk that obligations will
not be met when due. Financial protection factors will fluctuate widely
according to economic cycles, industry conditions and/or company fortunes.
Potential exists for frequent changes in the rating within this category or into
a higher or lower rating grade.

     CCC: Well below investment-grade securities. Considerable uncertainty
exists as to timely payment of principal, interest or preferred dividends.
Protection factors are narrow and risk can be substantial with unfavorable
economic/ industry conditions, and/or with unfavorable company developments.

     DD: Defaulted debt obligations. Issuer failed to meet scheduled principal
and/or interest payments.

     DP: Preferred stock with dividend arrearages.

                                       A-4


<PAGE>


                        Duff & Phelps Short-Term Ratings

     D-1+: Highest certainty of timely payment. Short-term liquidity, including
internal operation factors and/or access to alternative sources of funds, is
outstanding and safety is just below risk-free U.S. Treasury short-term
obligations.

     D-1: Very high certainty of timely payment. Liquidity factors are excellent
and supported by good fundamental protection factors. Risk factors are minor.

     D-1: High certainty of timely payment. Liquidity factors are strong and
supported by good fundamental protection factors. Risk factors are very small.

     D-2: Good certainty of timely payment. Liquidity factors and company
fundamentals are sound. Although ongoing funding needs may enlarge total
financing requirements, access to capital markets is good. Risk factors are
small.

     D-3: Satisfactory liquidity and other protection factors qualify issues as
to investment grade. Risk factors are larger and subject to more variation.
Nevertheless, timely payment is expected.

     D-4: Speculative investment characteristics. Liquidity is not sufficient to
insure against disruption in debt service. Operating factors and market access
may be subject to a high degree of variation.

     D-5: Issuer failed to meet scheduled principal and/or interest payments.

                                       A-5


<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
State Street Bank and Trust Company
225 Franklin Street, Boston, MA 02110

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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                                   PROSPECTUS

                                   May 1, 1998


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