A synthetic peptide cancer vaccine consisting of amino acid residues 209 through 217 of the glycoprotein 100 (gp100) melanoma antigen, with a methionine substitution at position 210 designed to improve immunogenicity. Vaccination with gp100:209-217(210M) peptide may stimulate the host immune system to mount a cytotoxic T lymphocyte (CTL) response against tumor cells expressing gp100.