A peptide vaccine consisting of the amino acids 280 through 288 of the melanoma antigen glycoprotein 100 (gp100) with potential antineoplastic activity. gp100:280-288(288V) peptide has a valine substitution at amino acid position 288 to improve immunogenicity. Vaccination with gp100:280-288(288V) peptide may stimulate the host immune system to mount a cytotoxic T lymphocyte (CTL) response against tumor cells positive for the gp100 antigen, resulting in decreased tumor growth.