<PAGE>
Supplement dated February 9, 2000
to the Prospectus for Class A Shares and Class B Shares
dated May 1, 1999, as supplemented
through January 18, 2000
of Flag Investors Real Estate Securities Fund, Inc.
The following replaces the "Example" on page 3 of the prospectus.
Example:
This Example is intended to help you compare the cost of investing in
each class of the Fund with the cost of investing in other mutual funds.
The Example assumes that you invest $10,000 in the Fund for the time
periods indicated and then redeem all of your shares at the end of those
periods. The Example also assumes that your investment has a 5% return each year
and that the Fund's operating expenses remain the same. Although your actual
costs may be higher or lower, based on these assumptions your costs would be:
1 year 3 years 5 years 10 years
------ ------- ------- --------
Class A Shares............. $670* $986* $1,325* $2,292*
Class B Shares............. $703* $991* $1,409* $2,369*
You would pay the following expenses if you did not redeem your shares:
Class A Shares............. $670* $986* $1,325* $2,292*
Class B Shares............. $203* $691* $1,209* $2,369*
- -------------
* Based on Total Annual Fund Operating Expenses after fee waivers and expense
reimbursements for year 1 only.
Federal regulations require that the table above reflect the maximum
sales charge. However, you may qualify for reduced sales charges or no sales
charge at all. (Refer to the section on sales charges.) If you hold your shares
for a long time, the combination of the initial sales charge you paid and the
recurring 12b-1 fees may exceed the maximum sales charges permitted by the
Conduct Rules of the National Association of Securities Dealers, Inc.
PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE
SUPRE (2/00)