<PAGE>
MFS(R) BOND FUND
Supplement dated September 1, 1999 (as revised October 1, 1999)
to the Current Prospectus
This Supplement describes the fund's class I shares, and it supplements
certain information in the fund's Prospectus dated September 1, 1999. The
caption headings used in this Supplement correspond with the caption headings
used in the Prospectus.
You may purchase class I shares only if you are an eligible institutional
investor, as described under the caption "Description of Share Classes" below.
1. RISK RETURN SUMMARY
Performance Table. The "Performance Table" is intended to indicate some of
the risks of investing in the fund by showing changes in the fund's performance
over time. The table is supplemented as follows:
Average Annual Total Returns as of December 31, 1998
1 Year 5 Years 10 Years
------ ------- --------
Class I shares 4.83% 6.98% 9.32%
Lehman Brothers Government/Corporate Bond Index+* 9.49% 7.31% 9.34%
Average corporate debt BBB-rated fund+ 6.23% 6.98% 9.16%
- -----------------
+ Source: Lipper Analytical Services, Inc.
* Lehman Brothers Government/Corporate Bond Index is a broad based unmanaged,
market-value-weighted index of all debt obligations of the U.S. Treasury
and U.S. government agencies (excluding mortgage-backed securities) and of
all publicly issued fixed-rate, nonconvertible, investment-grade domestic
corporate debt.
The fund commenced investment operations on May 8, 1974 with the offering
of class A shares, and subsequently offered class I shares on January 2, 1997.
Class I share performance includes the performance of the fund's class A shares
for periods prior to the offering of class I shares. This blended class I share
performance has been adjusted to take into account the fact that class I shares
have no initial sales charge (load). This blended performance has not been
adjusted to take into account differences in class specific operating expenses.
Because operating expenses of class I shares are lower than those of class A
shares, this blended class I share performance is lower than the performance of
class I shares would have been had class I shares been offered for the entire
period.
2. EXPENSE SUMMARY
Expense Table. The "Expense Table" describes the fees and expenses that you
may pay when you buy, redeem and hold shares of the fund. The table is
supplemented as follows:
Annual Fund Operating Expenses (expenses that are deducted from fund
assets):
Management Fees...................................... 0.38%
Distribution and Service (12b-1) Fees................ 0.00%
Other Expenses(1).................................... 0.27%
Total Annual Fund Operating Expenses................. 0.65%
- -----------------
(1) The fund has an expense offset arrangement which reduces the fund's
custodian fee based upon the amount of cash maintained by the fund with its
custodian and dividend disbursing agent. The fund may enter into other
similar arrangements and directed brokerage arrangements, which would also
have the effect of reducing the fund's expenses. "Other Expenses" do not
take into account these expense reductions, and therefore do not represent
the actual expenses of the fund.
3. EXAMPLE OF EXPENSES
The "Example of Expenses" table is intended to help you compare the cost of
investing in the fund with the cost of
1
<PAGE>
investing in other mutual funds.
These examples assume that:
o You invest $10,000 in the fund for the time periods indicated and you
redeem your shares at the end of the time periods;
o Your investment has a 5% return each year and dividends and other
distributions are reinvested; and
o The fund's operating expenses remain the same.
The table is supplemented as follows:
Share Class Year 1 Year 3 Year 5 Year 10
----------- ------ ------ ------ -------
Class I shares $66 $208 $362 $810
4. DESCRIPTIONS OF SHARE CLASSES
The "Description of Share Classes" is supplemented as follows:
If you are an eligible institutional investor (as described below), you may
purchase class I shares at net asset value without an initial sales charge or
CDSC upon redemption. Class I shares do not have annual distribution and service
fees, and do not convert to any other class of shares of the fund.
The following eligible institutional investors may purchase class I shares:
o certain retirement plans established for the benefit of employees of
MFS and employees of MFS' affiliates;
o any fund distributed by MFS, if the fund seeks to achieve its
investment objective by investing primarily in shares of the fund and
other MFS funds:
o any retirement plan, endowment or foundation which:
purchases shares directly through MFD (rather than through a
third party broker or dealer or other financial adviser),
has, at the time of purchase of class I shares, aggregate assets
of at least $100 million, and
invests at least $10 million in class I shares of the fund either
alone or in combination with investments in class I shares of
other MFS Funds (additional investments may be made in any
amount).
MFD may accept purchases from smaller plans, endowments or foundations
or in smaller amounts if it believes, in its sole discretion, that
such entity's aggregate assets will equal or exceed $100 million, or
that such entity will make additional investments which will cause its
total investment to equal or exceed $10 million, within a reasonable
period of time;
o bank trust departments or law firms acting as trustee or manager for
trust accounts which, on behalf of their clients (i) initially invest
at least $100,000 in class I shares of the fund or (ii) have, at the
time of purchase of class I shares, aggregate assets of at least $10
million invested in class I shares of the fund either alone or in
combination with investments in class I shares of other MFS Funds. MFD
may accept purchases that do not meet these dollar qualification
requirements if it believes, in its sole discretion, that these
requirements will be met within a reasonable period of time.
Additional investments may be made in any amount; and
2
<PAGE>
o certain retirement plans offered, administered or sponsored by
insurance companies, provided that these plans and insurance companies
meet certain criteria established by MFD from time to time.
In no event will the fund, MFS, MFD or any of their affiliates pay any
sales commissions or compensation to any third party in connection with the sale
of class I shares. The payment of any such sales commission or compensation
would, under the fund's policies, disqualify the purchaser as an eligible
investor in class I shares.
5. HOW TO PURCHASE, EXCHANGE AND REDEEM SHARES
The discussion of "How to Purchase, Exchange and Redeem Shares" is
supplemented as follows:
You may purchase, redeem and exchange class I shares only through your MFD
representative or by contacting MFSC (see the back cover of the Prospectus for
address and phone number). You may exchange your class I shares for class I
shares of another MFS Fund (if you are eligible to purchase them) and for shares
of the MFS Money Market Fund at net asset value.
6. FINANCIAL HIGHLIGHTS
The "Financial Highlights" table is intended to help you understand the
fund's financial performance. It is supplemented as follows:
Financial Statements - Class I shares
<TABLE>
<CAPTION>
<S> <C> <C> <C>
Year Ended Year Ended Period Ended
4/30/99 4/30/98 4/30/97*
---------- ---------- ------------
Per share data (for a share outstanding throughout each period):
Net asset value - beginning of period $ 13.58 $ 13.05 $ 13.15
Income from investment operations# -
Net investment income $ 0.92 $ 0.94 $ 0.31
Net realized and unrealized gain/(loss) on investments
and foreign currency (0.45) 0.55 (0.09)
--------- -------- ---------
Total from investment operations $ 0.47 $ 1.49 $ 0.22
Less distributions declared to shareholders -
From net investment income $ (0.92) $ (0.96) $ (0.32)
From net realized gain on investments and
foreign currency transactions (0.03) -- --
In excess of net investment income+++ -- (0.00) --
In excess of net realized gain on investments and
foreign currency (0.01) -- --
--------- -------- --------
Total distributions declared to shareholders $ (0.96) $ (0.96) $ (0.32)
--------- -------- --------
Net asset value - end of period $ 13.09 $ 13.58 $ 13.05
--------- -------- --------
Total return 3.56% 11.72% 1.70++
Ratios (to average net assets)/Supplemental data -
Expenses## 0.65% 0.68% 0.69%+
Net investment income 6.90% 6.95% 7.19%+
Portfolio turnover 343% 333% 446%
Net assets at end of period (000 omitted) $9,256 $9,249 $9,593
</TABLE>
- -----------------
* For the period from the inception of Class I, January 2, 1997, through
April 30, 1997.
+ Annualized.
++ Not annualized.
+++ For the year ended April 30, 1998, the per share distribution in excess of
net investment income was less than $0.01.
# Per share data are based on average shares outstanding.
## The fund has an expense offset arrangement which reduces the fund's
custodian fee based upon the amount of cash maintained by the fund with its
custodian and dividend disbursing agent. The Fund's expenses are calculated
without reduction for this expense offset arrangement.
The date of this Supplement is September 1, 1999 (as revised October 1, 1999).
3
