Tumor rejection antigens, recognized by cytotoxic T lymphocytes (CTL), have been identified in several tumors. In malignant melanoma MAGE-1 and -3 antigen peptides, recognized by specific CTL, were defined. Tyrosinase, gp100 and Melan A/MART-1, normally expressed in the melanosome, were also shown to be recognized by specific CTL. In murine tumors, three antigenic peptides were identified. These are P1A in mastocytoma P815, MUT1 in murine lung carcinoma (3LL) derived from connexin 37, and pRL1 in murine leukemia RL male 1 derived from c-akt proto-oncogene. Analysis of the tumor rejection antigen peptides will elucidate the molecular nature of the tumor rejection antigen and facilitate their therapeutic use as tumor vaccine.