Summary:Melan-A/MART-1 is a recently identified new melanocytic differentiation marker, which is recognized as an antigen on melanoma cells by cytotoxic Tlymphocytes. It is of interest for clinicians as potential immunotherapeutic target and it is relevant for pathologists as a novel diagnostic marker, since two antibodies (A 103 and M2-7C10) have become available to study Melan-A/MART-1 expression on archival material. Both antibodies are useful in the differential diagnosis of melanocytic tumors, especially metastatic tumors, since they are more sensitive than HMB-45. Both antibodies are also of diagnostic value in the recognition of perivascular epithelioid cell tumors (angiomyolipoma, lymphangioleiomyomatosis, and clear cell tumor). Since A103 has the unique property of staining many steroid hormone producing cells, this antibody is also of value for the recognition of tumors derived from these cells, such as adrenocortical carcinomas. Both antibodies are likely to be included in the routine diagnostic armamentarium of many immunohistochemical laboratories in the near future.