MART-1, also known as Melan A or Melanoma Antigen Recognized by T Cells 1, is a protein antigen found specifically on melanocytes of normal skin, retina, and nevi, and not in other normal tissues. It is a type III membrane protein with a molecular weight of 22-24 kDa. It is present in the endoplasmic reticulum (ER), trans-Golgi network (TGN). MART-1 is a melanocyte lineage protein.

MART-1 labels both normal melanocyte and diseased cell with melanocyte differentiation. It is useful for diagnosis of tumors with melanocyte differentiation, especially metastatic melanoma. Identification of MART-1 also opens possibilities for the development of immunotherapies for patients with melanoma. Anti-MART-1 (Melan A) is therefore useful as a marker for melanocytic tumors, and as an aid in establishing the diagnosis of metastatic melanomas.