The HOM‐MEL‐40 antigen which is encoded by the SSX‐2 gene was originally detected as a tumor antigen recognized by autologous IgG antibodies in a melanoma patient. Expression analysis demonstrated that SSX‐2 is a member of the recently described cancer/testis antigen (CTA) class as it is expressed in a variety of different human neoplasms, but not in normal tissues with the exception of testis and a weak expression in the thyroid. Further studies demonstrated that SSX‐2 belongs to a gene family consisting of at least 5 homologous genes. We now report the analysis of the expression of all 5 SSX genes in 325 specimens of human neoplasms from various histological origins, using reverse transcription polymerase chain reaction (RT‐PCR). SSX‐1, ‐2, and ‐4 were found to be expressed in 8%, 15% and 15%, of the tumors, respectively, while the expression of the SSX‐5 gene was rare (7/325), and SSX‐3 expression was not detected. For defined tumor types, expression of at least one of the SSX family members was most frequently observed in head and neck cancer (75%), followed by ovarian cancer (50%), malignant melanoma (43%), lymphoma (36%), colorectal cancer (27%) and breast cancer (23%), while leukemias and the few cases of leiomyosarcomas, seminomas and thyroid cancers were found not to express any SSX gene. Int. J. Cancer 77:19–23, 1998.© 1998 Wiley‐Liss, Inc.