CERTIFICATIONS PURSUANT TO SECTION 906
EX-99.906CERT

                                  CERTIFICATION

R. Jay Gerken, Chief Executive Officer, and Richard L. Peteka, Chief Financial
Officer of Smith Barney Investment Series - Smith Barney Premier Selections All
Cap Growth Portfolio (the "Registrant"), each certify to the best of his or her
knowledge that:

1. The Registrant's periodic report on Form N-CSR for the period ended October
31, 2003 (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 Financial Officer
Smith Barney Investment Series -            Smith Barney Investment Series -
Smith Barney Premier Selections             Smith Barney Premier Selections
       All Cap Growth Portfolio                    All Cap Growth Portfolio

/s/ R. Jay Gerken                           /s/ Richard L. Peteka
- ---------------------------                 ---------------------------
R. Jay Gerken                               Richard L. Peteka
Date:  December 29, 2003                    Date:  December 29, 2003

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



CERTIFICATIONS PURSUANT TO SECTION 906
EX-99.906CERT


                                  CERTIFICATION

R. Jay Gerken, Chief Executive Officer, and Richard L. Peteka, Chief Financial
Officer of Smith Barney Investment Series - Smith Barney Large Cap Core
Portfolio (the "Registrant"), each certify to the best of his or her knowledge
that:

  1. The Registrant's periodic report on Form N-CSR for the period ended October
31, 2003 (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 Financial Officer
Smith Barney Investment Series -           Smith Barney Investment Series -
Smith Barney Large Cap Core Portfolio      Smith Barney Large Cap Core Portfolio

/s/ R. Jay Gerken                          /s/ Richard L. Peteka
- ---------------------------                ---------------------------
R. Jay Gerken                              Richard L. Peteka
Date:   December 29, 2003                  Date:  December 29, 2003


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



CERTIFICATIONS PURSUANT TO SECTION 906
EX-99.906CERT

                                  CERTIFICATION

R. Jay Gerken, Chief Executive Officer, and Richard L. Peteka, Chief Financial
Officer of Smith Barney Investment Series - Smith Barney Growth and Income
Portfolio (the "Registrant"), each certify to the best of his or her knowledge
that:

1. The Registrant's periodic report on Form N-CSR for the period ended October
31, 2003 (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 Financial Officer
Smith Barney Investment Series -            Smith Barney Investment Series -
Smith Barney Growth and Income Portfolio    Smith Barney Growth and Income Portfolio


/s/ R. Jay Gerken                           /s/ Richard L. Peteka
- ---------------------------                 ---------------------------
R. Jay Gerken                               Richard L. Peteka
Date:  December 29, 2003                    Date:  December 29, 2003

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



CERTIFICATIONS PURSUANT TO SECTION 906
EX-99.906CERT

                                  CERTIFICATION

R. Jay Gerken, Chief Executive Officer, and Richard L. Peteka, Chief Financial
Officer of Smith Barney Investment Series - SB Government Portfolio (the
"Registrant"), each certify to the best of his or her knowledge that:

1. The Registrant's periodic report on Form N-CSR for the period ended October
31, 2003 (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 Financial Officer
Smith Barney Investment Series -            Smith Barney Investment Series -
SB Government Portfolio                     SB Government Portfolio



/s/ R. Jay Gerken                           /s/ Richard L. Peteka
- ---------------------------                 ---------------------------
R. Jay Gerken                               Richard L. Peteka
Date:  December 29, 2003                    Date:  December 29, 2003

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