Melanoma-associated antigens extracted from cultured human melanoma cells or isolated from their spent culture medium react specifically with monoclonal antibody and are represented by glycoproteins with molecular weights of 260,000 (260K), 250,000 (250K), and 100,000 (100K). The 260 and 250K antigens are present only in spent culture medium or detergent extracts of melanoma cells, respectively. The 100K antigen is an oncofetal marker present on tumor cells of different histological type. Indirect immunofluorescence data indicate that the 250K antigen is present on the surface of melanoma cells from excised melanoma tissues when the 100K antigen appears to be present in the cytosol. Subunit structure determination indicates that the 100K antigen is a single polypeptide chain whereas the 250K antigen extracted from melanoma cells is associated with a proteoglycan fragment which is important for its cell surface expression.