A recombinant nonapeptide used as an antineoplastic vaccine. NY-ESO-1b peptide vaccine contains the amino acid sequence SLLMWITQC, derived from the cancer-testis tumor antigen (NY-ESO-1), which is expressed on tumor cells of many different types, including melanomas. Vaccination with this peptide vaccine may elicit strong humoral and cellular immune responses to NY-ESO-1-expressing cancers.