The color of mammalian hair, skin, and eyes results mainly from the secretory products of melanocytes. These secretory products consist of a wide range of melanin pigments with different structures and compositions. These include black or brown nitrogenous eumelanins; yellow or reddish brown, sulfur-containing pheomelanins, e.g., the trichochromes of low molecular weight; and other pigments whose chemical and physical properties are intermediate between those of typical eumelanins and pheomelanins. Despite the evident differences in molecular size and general properties, all these pigments are biogenetically related, and they arise from a common metabolic pathway in which dopaquinone is the key intermediate. The current state of knowledge on the molecular mechanisms governing the metabolic fate of dopaquinone in melanocytes is discussed with special reference to the role of such sulfhydryl compounds as cysteine and glutathione in melanogenesis.