MART-1 (Melanoma Antigen Recognized by T cells 1) or Melan-A1 is a newly identified melanocyte differentiation antigen recognized by autologous cytotoxic T lymphocytes. MART-1 is present in melanosomes and endoplasmic reticulum. Clone 103 does not cross-react with MAGE-1 or tyrosinase protein. Clone 103 labels melanomas and other tumors showing melanocytic differentiation. It does not stain tumor cells of epithelial, lymphoid, glial, or mesenchymal origin.