CERTIFICATIONS PURSUANT TO SECTION 906
EX-99.906CERT

                                  CERTIFICATION

R. Jay Gerken, Chief Executive Officer, and Andrew B. Shoup, Chief
Administrative Officer of Smith Barney Investment Series - Smith Barney Large
Cap Core Fund (the "Registrant"), each certify to the best of his knowledge
that:

1.      The Registrant's periodic report on Form N-CSR for the period ended
        April 30, 2004 (the "Form N-CSR") fully complies with the requirements
        of section 15(d) of the Securities Exchange Act of 1934, as amended; and

2.      The information contained in the Form N-CSR fairly presents, in all
        material respects, the financial condition and results of operations of
        the Registrant.


Chief Executive Officer                     Chief Administrative Officer
Smith Barney Investment Series -            Smith Barney Investment Series -
Smith Barney Large Cap Core Fund            Smith Barney Large Cap Core Fund


/s/ R. Jay Gerken                           /s/ Andrew B. Shoup
- ---------------------------                 ------------------------------------
R. Jay Gerken                               Andrew B. Shoup
Date: June 30, 2004                         Date: June 30, 2004

This certification is being furnished to the Securities and Exchange Commission
solely pursuant to 18 U.S.C. Section 1350 and is not being filed as part of the
Form N-CSR with the Commission.