ROBECO INVESTMENT FUNDS

                     INSTITUTIONAL CLASS AND INVESTOR CLASS

                            ROBECO WPG CORE BOND FUND
                        ROBECO WPG LARGE CAP GROWTH FUND
                              ROBECO WPG TUDOR FUND

                         Supplement dated August 8, 2005
                       to Prospectuses dated March 9, 2005

THIS SUPPLEMENT CONTAINS NEW AND ADDITIONAL INFORMATION BEYOND THAT CONTAINED IN
THE PROSPECTUS AND SHOULD BE READ IN CONJUNCTION WITH THE PROSPECTUS.

         THE  SUB-PARAGRAPH  ENTITLED  "REDEMPTION  BY TELEPHONE" IN THE SECTION
ENTITLED "REDEMPTION OF FUND SHARES" ON PAGE 18 OF THE INVESTOR CLASS PROSPECTUS
AND ON PAGE 30 OF THE INSTITUTIONAL  CLASS PROSPECTUS IS REMOVED IN ITS ENTIRETY
AND REPLACED WITH THE FOLLOWING:


         REDEMPTION  BY TELEPHONE.  In order to request a telephone  redemption,
you must have returned your account application containing a telephone election.
To add a  telephone  redemption  option  to an  existing  account,  contact  the
Transfer Agent by calling (800) 223-3332.

         Once you are authorized to utilize the telephone  redemption  option, a
redemption  of Shares may be requested  by calling the  Transfer  Agent at (800)
223-3332 and requesting  that the  redemption  proceeds be mailed to the primary
registration address or wired per the authorized instructions.  A wire charge of
$7.50 is assessed and charged to the  shareholder.  If the telephone  redemption
option or the telephone  exchange  option is authorized,  the Transfer Agent may
act on telephone instructions from any person representing himself or herself to
be a shareholder and believed by the Transfer Agent to be genuine.  The Transfer
Agent's  records of such  instructions  are  binding and  shareholders,  not the
Company  or  the  Transfer  Agent,  bear  the  risk  of  loss  in the  event  of
unauthorized  instructions  reasonably  believed by the Company or the  Transfer
Agent to be genuine.  The Company and the Transfer Agent will employ  reasonable
procedures to confirm that instructions communicated are genuine and, if it does
not,  it may  be  liable  for  any  losses  due to  unauthorized  or  fraudulent
instructions.  The procedures  employed by the Company and the Transfer Agent in
connection with  transactions  initiated by telephone  include tape recording of
telephone instructions and requiring some form of personal  identification prior
to acting upon instructions received by telephone.



               PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE.