Variants of the Bomirski family of hamster melanomas whose proliferative rates differ inversely with the genetically determined degree of melanogenesis were probed for two proteins critical in melanogenesis: tyrosinase and catalase-B (gp 75). The parental black tumor Ma contained both proteins in abundance. The amelanotic variant Ab, inducible in culture with L-tyrosine or L-dopa to form melanosomes and to melanize, had minimal tyrosinase, despite high levels of (tyr)mRNA, and no gp 75. Variant MI, hypomelanotic despite abundant tyrosinase, and synthesizing predominantingly pheo-(red) melanin, expressed barely detectable gp 75. These findings suggest a regulatory control of melanogenesis distal to (tyr)mRNA and strengthen the hypothesis that in vivo tyrosinase without catalase-B favors pheo- over eumelanogenesis.