Melanocyte lineage-specific antigens, like gp100, have been shown to be recognized by tumour-infiltrating lymphocytes isolated from melanoma patients. Therefore these antigens might be used as targets for specific anti-melanoma immunotherapy. To investigate this potential in syngeneic mouse models, we cloned and characterized the murine homologue of gp100 from a B16 murine melanoma cDNA library. The isolated cDNA clone encodes a protein of 626 amino acids, sharing 79.7% sequence homology with human gp100. Expression of murine gp100 was restricted to cells of the melanocyte lineage, as determined by Northern and Western analysis. However, like human gp100, reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed low levels of transcription of the murine gp100 gene in all the cell lines and normal tissues tested. In contrast, murine tyrosinase, another melanocyte differentiation antigen, mimics human tyrosinase expression and did show absolute melanocyte lineage-specific expression. The characterization of murine gp100 will allow investigation of anti-gp100 immune responses in C57BL/6 mice using the syngeneic B16 tumour model and the possible adverse effects of such immunity on normal melanocytes.