The Drosophila melanogaster diphenol oxidase (DOX) A2-encoding gene (Dox-A2) is involved in catecholamine metabolism, melanin formation and sclerotization of the cuticle. Insect phenol oxidases (POX) are well studied biochemically, but not genetically and molecularly. The Dox-A2 (2-53.9) gene is the first insect POX-encoding gene to be cloned and sequenced. It encodes a protein product unique among currently known POX. The deduced protein, however, exhibits extensive similarity (58-81%) to the mouse mast cell tum- antigen, P91A [Lurquin et al., Cell 58 (1989) 293-303] and may identify the normal mouse protein as a DOX.