<PAGE>
SALOMON BROTHERS INVESTMENT SERIES
7 WORLD TRADE CENTER
NEW YORK, NEW YORK 10048
(888) 777-0102
SUPPLEMENT DATED SEPTEMBER 14, 1998 TO THE PROSPECTUS DATED MAY 1, 1998
The information contained in this prospectus supplement amends, and to the
extent inconsistent therewith, supersedes information contained in the
Prospectus. The pricing and conversion changes described herein with respect
to the Multiple Pricing System are not applicable to (i) shares purchased
prior to September 14, 1998, (ii) shares purchased with reinvested dividend or
capital gain distributions relating to shares purchased prior to September 14,
1998, or (iii) shares of a Fund acquired as the result of an exchange of
shares purchased prior to September 14, 1998.
The following information replaces in its entirety the information on page 9
in the section of the prospectus entitled "Expense Information":
EXPENSE INFORMATION
Each Fund offers multiple classes of shares. Each share of a Fund accrues
income in the same manner, but certain expenses differ based upon the class.
The following tables are intended to assist investors in understanding the
various costs and expenses borne by each class of shares of each Fund:
<TABLE>
<CAPTION>
CLASS A CLASS B CLASS 2 CLASS O(D)
-------------- ---------------------- --------- ----------
<S> <C> <C> <C> <C>
SHAREHOLDER TRANSACTION
EXPENSES*
Maximum Sales Charge
Imposed on Purchases of
Shares (as a percentage
of offering price)
Total Return, Small
Cap Growth, Asia
Growth, Investors and
Capital Funds........ 5.75%(a) None 1.00% None
National Intermediate
Municipal, U.S.
Government Income,
High Yield Bond and
Strategic Bond Funds. 4.75%(a) None 1.00% None
Cash Management Fund.. None None None None
New York Municipal
Money Market Fund.... None None None None
Sales Charge Imposed on
Reinvested Dividends
All Funds............. None None None None
Contingent Deferred
Sales Charge (as a
percentage of original
purchase price or
redemption price,
whichever is lower)
All Funds except Cash
Management Fund and
New York Municipal
Money Market Fund.... 1% during the 5% first year, 1% during None
first year for 4% second year the first
purchases of 3% third year, year(a)
$1 million or 2% fifth year,
more (b) 1% sixth year
0% after sixth year(c)
Cash Management Fund.. None None None None
New York Municipal
Money Market Fund.... None None None None
</TABLE>
S-1
<PAGE>
<TABLE>
<CAPTION>
CLASS A CLASS B CLASS 2 CLASS O(D)
------- ------- ------- ----------
<S> <C> <C> <C> <C>
Redemption Fees
All Funds.................................. None None None None
Exchange Fee
All Funds.................................. None None None None
</TABLE>
- --------
(a) Reduced for purchases of $50,000 and over, decreasing to 0% for purchases
of $1,000,000 and over. See "Purchase of Shares--Class A Shares."
(b) See "Purchase of Shares--Class A Shares" and "Redemption of Shares--Class
A Shares."
(c) See "Purchase of Shares--Class B Shares" and "--Class C Shares" and
"Redemption of Shares--Class B Shares" and "--Class C Shares."
(d) Only Class O shareholders are permitted to purchase additional Class O
shares.
* Under certain circumstances, certain broker-dealers may impose additional
transaction fees on the purchase and/or sale of shares. See "Purchase of
Shares."
----------------
The following information replaces in its entirety the information under the
caption "Example" in the section of the Prospectus entitled "Expense
Information:"
EXAMPLE:
The following table demonstrates the projected dollar amount of total
cumulative expenses that would be incurred over various periods with respect
to a hypothetical investment in each class of each Fund. The example assumes
payment by each Fund of operating expenses at the levels set forth in the
preceding table and are also based upon the following assumptions:
An investor would pay the following expenses on a $1,000 investment,
assuming: (1) 5% annual return; and (2) redemption at the end of each time
period, with the exception of the lines marked "Class B No redemption," in
which case it is assumed that no redemption is made at the end of each time
period:
<TABLE>
<CAPTION>
FUND 1 YEAR 3 YEARS 5 YEARS 10 YEARS
- ---- ------ ------- ------- --------
<S> <C> <C> <C> <C>
CASH MANAGEMENT
Class A Shares............................. $ 6 $18 $ 31 $ 69
Class B Shares............................. $ 6 $18 $ 31 $ 69
Class 2 Shares............................. $ 6 $18 $ 31 $ 69
Class O Shares............................. $ 6 $18 $ 31 $ 69
NEW YORK MUNICIPAL MONEY MARKET
Class A Shares............................. $ 5 $16 $ 28 $ 63
Class B Shares............................. $ 4 $14 $ 24 $ 54
Class 2 Shares............................. $ 5 $16 $ 28 $ 63
Class O Shares............................. $ 4 $14 $ 24 $ 54
NATIONAL INTERMEDIATE MUNICIPAL
Class A Shares*............................ $55 $70 $ 87 $136
Class B Shares***.......................... $65 $77 $102 $149****
Class B No redemption...................... $15 $47 $ 82 $149****
Class 2 Shares***.......................... $35 $57 $ 91 $187
Class O Shares............................. $ 5 $16 $ 28 $ 63
U.S. GOVERNMENT INCOME
Class A Shares*............................ $56 $73 $ 92 $148
Class B Shares***.......................... $66 $80 $107 $160****
</TABLE>
S-2
<PAGE>
<TABLE>
<CAPTION>
FUND 1 YEAR 3 YEARS 5 YEARS 10 YEARS
- ---- ------ ------- ------- --------
<S> <C> <C> <C> <C>
Class B No redemption....................... $16 $ 50 $ 87 $160****
Class 2 Shares***........................... $36 $ 60 $ 96 $197
Class O Shares.............................. $ 6 $ 19 $ 33 $ 75
HIGH YIELD BOND
Class A Shares*............................. $60 $ 85 $112 $191
Class B Shares***........................... $70 $ 92 $127 $203****
Class B No redemption....................... $20 $ 62 $107 $203****
Class 2 Shares***........................... $40 $ 72 $116 $240
Class O Shares.............................. $10 $ 32 $ 55 $121
STRATEGIC BOND
Class A Shares*............................. $60 $ 85 $112 $191
Class B Shares***........................... $70 $ 92 $127 $203****
Class B No redemption....................... $20 $ 62 $107 $203****
Class 2 Shares***........................... $40 $ 72 $116 $240
Class O Shares.............................. $10 $ 31 $ 53 $118
TOTAL RETURN
Class A Shares**............................ $66 $ 83 $102 $157
Class B Shares***........................... $66 $ 80 $107 $160****
Class B No redemption....................... $16 $ 50 $ 87 $160****
Class 2 Shares***........................... $36 $ 60 $ 96 $198
Class O Shares.............................. $ 6 $ 19 $ 33 $ 75
SMALL CAP GROWTH
Class A Shares**............................ $72 $102 $135 $227
Class B Shares***........................... $73 $100 $140 $231****
Class B No redemption....................... $23 $ 70 $120 $231****
Class 2 Shares***........................... $43 $ 80 $129 $266
Class O Shares.............................. $10 $ 32 $ 55 $122
ASIA GROWTH
Class A Shares**............................ $69 $ 95 $122 $199
Class B Shares***........................... $70 $ 92 $127 $203****
Class B No redemption....................... $20 $ 62 $107 $203****
Class 2 Shares***........................... $40 $ 72 $116 $240
Class O Shares.............................. $10 $ 32 $ 55 $121
INVESTORS
Class A Shares**............................ $67 $ 86 $107 $168
Class B Shares***........................... $67 $ 84 $112 $172****
Class B No redemption....................... $17 $ 54 $ 92 $172****
Class 2 Shares***........................... $37 $ 63 $101 $209
Class O Shares.............................. $ 7 $ 22 $ 38 $ 86
CAPITAL
Class A Shares**............................ $72 $101 $133 $222
Class B Shares***........................... $72 $ 99 $138 $226****
Class B No redemption....................... $22 $ 69 $118 $226****
Class 2 Shares***........................... $42 $ 79 $127 $262
Class O Shares.............................. $12 $ 39 $ 67 $148
</TABLE>
S-3
<PAGE>
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* Assumes deduction at the time of purchase of the maximum 4.75% sales
charge.
** Assumes deduction at the time of purchase of the maximum 5.75% sales
charge.
*** Assumes deduction at the time of redemption of the maximum CDSC
applicable for that time period.
**** Reflects the conversion to Class A shares seven years after purchase, and
therefore years eight through ten reflect Class A expenses.
THIS EXAMPLE SHOULD NOT BE CONSIDERED AS REPRESENTATIVE OF PAST OR FUTURE
EXPENSES AND ACTUAL EXPENSES FOR ANY OF THE FUNDS MAY BE HIGHER OR LOWER THAN
THE AMOUNTS SHOWN. Moreover, while the example assumes a 5% annual return,
each Fund's performance will vary and may result in a return greater or less
than 5%.
The information in the foregoing summary is qualified in its entirety by the
more detailed information appearing elsewhere in this Prospectus and in the
Statement of Additional Information.
----------------
The following information replaces the "Class A Sales Charge Table" under
the caption "Class A Shares" in the section of the Prospectus entitled
"Purchase of Shares:"
CLASS A SALES CHARGE TABLE--TOTAL RETURN, SMALL CAP GROWTH,
ASIA GROWTH, INVESTORS AND CAPITAL FUNDS
<TABLE>
<CAPTION>
CONCESSION TO
PERCENTAGE OF BROKER-DEALER AS
AMOUNT OF PERCENTAGE OF THE NET AMOUNT A PERCENTAGE OF
PURCHASE PAYMENT THE OFFERING PRICE INVESTED OFFERING PRICE
---------------- ------------------ -------------- ----------------
<S> <C> <C> <C>
Less than $50,000........ 5.75% 6.10% 5.00%
$50,000 but less than
$100,000................ 4.50% 4.71% 4.00%
$100,000 but less than
$250,000................ 4.00% 4.17% 3.50%
$250,000 but less than
$500,000................ 2.75% 2.83% 2.50%
$500,000 but less than 1
million................. 2.00% 2.04% 1.75%
$1 million or more....... None* None **
</TABLE>
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* With respect to purchases of Class A shares of $1 million or more, a CDSC
will apply if the shares are redeemed within one year after purchase. See
"Redemption of Shares--Class A Share Purchases of $1 Million or More."
** The Distributor may in its discretion compensate selected dealers in
connection with the sale of Class A shares in an aggregate amount of $1
million or more up to the following amounts:
<TABLE>
<CAPTION>
DEALER'S
AMOUNT OF PURCHASE CONCESSION
------------------ ----------
<S> <C>
$1 million but less than $3 million........... 1.00%
$3 million but less than $5 million........... .50%
More than $5 million.......................... .25%
</TABLE>
S-4
<PAGE>
CLASS A SALES CHARGE TABLE--NATIONAL INTERMEDIATE MUNICIPAL, U.S. GOVERNMENT
INCOME, HIGH YIELD BOND AND STRATEGIC BOND FUNDS
<TABLE>
<CAPTION>
CONCESSION TO
PERCENTAGE OF BROKER-DEALER AS
AMOUNT OF PERCENTAGE OF THE NET AMOUNT A PERCENTAGE OF
PURCHASE PAYMENT THE OFFERING PRICE INVESTED OFFERING PRICE
---------------- ------------------ -------------- ----------------
<S> <C> <C> <C>
Less than $50,000........ 4.75% 4.99% 4.25%
$50,000 but less than
$100,000................ 4.50% 4.71% 4.00%
$100,000 but less than
$250,000................ 4.00% 4.17% 3.50%
$250,000 but less than
$500,000................ 2.75% 2.83% 2.50%
$500,000 but less than 1
million................. 2.25% 2.30% 2.00%
$1 million or more....... None* None **
</TABLE>
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* With respect to purchases of Class A shares of $1 million or more, a CDSC
will apply if the shares are redeemed within one year after purchase. See
"Redemption of Shares--Class A Share Purchases of $1 million or more."
** The Distributor may in its discretion compensate selected dealers in
connection with the sale of Class A shares in an aggregate amount of $1
million or more up to the following amounts:
<TABLE>
<CAPTION>
DEALER'S
AMOUNT OF PURCHASE CONCESSION
------------------ ----------
<S> <C>
$1 million but less than $3 million........................... 1.00%
$3 million but less than $5 million........................... .50%
More than $5 million.......................................... .25%
</TABLE>
----------------
The following information replaces the "Class B CDSC Table" under the
caption "Class B Shares" in the section of the Prospectus entitled "Redemption
of Shares:"
CLASS B CDSC TABLE
<TABLE>
<CAPTION>
CDSC
AS A PERCENTAGE
OF DOLLAR
AMOUNT SUBJECT
YEAR(S) SINCE PURCHASE ORDER TO CHARGE
---------------------------- ---------------
<S> <C>
1st year................................................. 5%
1 year or more but less than 2 years..................... 4%
2 years or more but less than 4 years.................... 3%
4 years or more but less than 5 years.................... 2%
5 years or more but less than 6 years.................... 1%
6 or more years.......................................... 0%
</TABLE>
Class B shares will convert to Class A shares at the end of the seventh year
after purchase.
----------------
Class C shares of each Fund have been renamed Class 2 shares. Class 2 shares
are subject to a 1% front end sales charge payable at the time of purchase, a
1% contingent deferred sales charge if shares are redeemed within one year of
purchase, and do not convert to Class A shares.
----------------
Class B and Class C shares of a Fund purchased prior to September 14, 1998
will continue to be subject to the CDSC schedules and conversion features in
effect at the time such purchase was made. Shares purchased with reinvested
dividend or capital gain distributions relating to shares purchased prior to
September 14, 1998 will be subject to the CDSC schedules and conversion
features in effect at the time the original shares were purchased. Shares of a
Fund acquired as result of an exchange of shares purchased prior to September
14, 1998 will also be subject to the CDSC schedules and conversion features in
effect at the time the original shares were purchased.
S-5
<PAGE>
There is no investment maximum for Class B or Class C shares. Please see
"Factors for Consideration" in the section of the Prospectus entitled
"Multiple Pricing System" for a discussion of the factors a shareholder should
consider in determining which class of shares of a Fund to purchase.
----------------
The following information supplements and should be read in conjunction with
the information contained under the caption "Distribution Fees" in the section
of the Prospectus entitled "Purchase of Shares:"
With respect to Class B shares, the Distributor will pay broker-dealers
at the time of sale a commission of 4% of the purchase price and a
quarterly trail fee at an annual rate of 0.25% which will begin to accrue
in the first month after settlement. With respect to Class 2 shares, the
Distributor will pay broker-dealers at the time of sale a commission of 2%
of the purchase price and a quarterly trail fee at an annual rate of 1%
which will begin to accrue in the thirteenth month after settlement.
----------------
The following information supplements and should be read in conjunction with
the information contained under the caption "Minimum Investment" in the
section of the Prospectus entitled "Purchase of Shares:"
The minimum initial investment in any class of shares of a Fund is $250.
----------------
The following information supplements and should be read in conjunction with
the information contained under the caption "Letter of Intent" in the section
of the Prospectus entitled "Purchase of Shares:"
Shareholders who purchased Class A shares of a Fund pursuant to a letter
of intent received prior to September 14, 1998 may make additional Class A
share purchases subject to the Class A sales charge table in effect prior
to September 14, 1998, until such time as the letter of intent goal has
been met.
----------------
The following information supplements and should be read in conjunction with
the information contained on the cover page of the Prospectus:
MUTUAL FUND SHARES ARE NOT DEPOSITS OR OBLIGATIONS OF, OR GUARANTEED OR
ENDORSED BY, ANY BANK, AND ARE NOT FEDERALLY INSURED BY THE FEDERAL DEPOSIT
INSURANCE CORPORATION, THE FEDERAL RESERVE BOARD, OR ANY OTHER AGENCY.
MUTUAL FUND SHARES INVOLVE CERTAIN INVESTMENT RISKS, INCLUDING THE POSSIBLE
LOSS OF PRINCIPAL. THE NET ASSET VALUE OF FUNDS OF THIS TYPE WILL FLUCTUATE
FROM TIME TO TIME.
----------------
The following information supplements and should be read in conjunction with
the information contained under the caption "Stripped Mortgage Securities" in
the section of the Prospectus entitled "Additional Investment Activities and
Risk Factors:"
The U.S. Government Income Fund may purchase stripped mortgage securities
which are derivative multiclass mortgage securities.
S-6
<PAGE>
----------------
The following information supplements and should be read in conjunction with
the information contained under the caption "Investment Manager" in the
section of the Prospectus entitled "Management:"
Roger Lavan is primarily responsible for the day-to-day management of the
U.S. Government Income Fund and the Strategic Bond Fund.
Thomas A. Croak and Robert E. Amodeo are primarily responsible for the
day-to-day management of the National Intermediate Municipal Fund. Mr.
Croak, who joined SBAM in 1995, is a Vice President of SBAM. Mr. Croak
joined Salomon Brothers in 1991. Mr. Amodeo, who joined SBAM in 1992, is a
Vice President of SBAM. Mr. Amodeo joined Salomon Brothers in 1988.
Charles K. Bardes and Thomas A. Croak are primarily responsible for the
day-to-day management of the New York Municipal Money Market Fund. Mr.
Bardes, who joined SBAM in 1988, is a Vice President of SBAM. Mr. Bardes
joined Salomon Brothers in 1986. Mr. Croak, who joined SBAM in 1995, is a
Vice President of SBAM. Mr. Croak joined Salomon Brothers in 1991.
George J. Williamson is primarily responsible for the day-to-day
management of the Total Return Fund. Mr. Williamson, who joined SBAM in
1990, is a Vice President of SBAM.
----------------
Effective September 1, 1998, CFBDS, Inc., a registered broker-dealer and an
indirect wholly-owned subsidiary of Signature Financial Group, Inc., serves as
each Fund's distributor.
The U.S. Government Income Fund may purchase stripped mortgage securities
which are derivative multiclass mortgage securities.
S-7
