The MAGE-1 gene codes for a tumor-specific antigen, MZ2-E, that elicited a cytotoxic T-lymphocyte response in the melanoma patient from whom it was derived. We have developed a simplified method, using polymerase chain reaction amplification of exon 3 followed by restriction enzyme pattern analysis, to distinguish expression of the MAGE-1 gene from MAGE-2 and MAGE-3, other members of this gene family. MAGE-1 mRNA was expressed in 53% of 17 melanoma lines, two of seven Epstein-Barr virus-transformed B-cell lines, and 2 of 5 breast cell lines including a line established form normal breast epithelium. MAGE-1 is not likely to be the common melanoma antigen recognized by the other HLA-A1- or HLA-A2-restricted cytotoxic T-lymphocytes examined in this study, but the fact that it is expressed in about 50% of melanoma cell lines makes it a reasonable target for the immunotherapy of patients bearing HLA-A1.