SECTION 906 CERTIFICATION

Pursuant to 18 U.S.C.ss.  1350, the undersigned officers of Federated Investment
Series Funds, Inc. on behalf of Federated Bond Fund (the  "Registrant"),  hereby
certify,  to the best of our  knowledge,  that the  Registrant's  Report on Form
N-CSR for the period ended November 30, 2004 (the "Report")  fully complies with
the requirements of Section 13(a) or 15(d), as applicable, of the Securities and
Exchange Act of 1934 and that the  information  contained  in the Report  fairly
presents,  in all material  respects,  the  financial  condition  and results of
operations of the Registrant.


Dated: January 24, 2005

/s/ J. Christopher Donahue

Title: President, Principal Executive Officer



Dated: January 24, 2005

/s/ Richard J. Thomas

Title: Treasurer, Principal Financial Officer

This certification is being furnished solely pursuant to 18 U.S.C.ss. 1350 and
is not being filed as part of the Report or as a separate disclosure document.