We have established two new immortal lines of mouse melanocytes, melan-b and melan-c, from mice homozygous for the brown (b) and albino (c) mutations respectively. Both lines were derived through differentiation in vitro of embryonic epidermal melanoblasts. The brown melanocytes are visibly brown by light microscopy, and centrifuged cell suspensions form brown pellets. The albino melanocytes form white pellets and contain abundant unpigmented premelanosomes as shown by transmission electron microscopy. Like normal, non-immortal melanocytes and like the immortal black melanocyte line melan-a, both lines show little or no growth in a standard, serum-supplemented medium, but proliferate well in the presence of 12-o-tetradecanoyl phorbol-13-acetate (TPA). Sustained growth of the albino cells also requires either keratinocyte feeder cells or 2-mercaptoethanol (2-ME). The modal chromosome numbers are 39 for melan-b and 40 (diploid) for melan-c. Neither line is tumorigenic in nude mice. Hetero-karyons between the two lines can be constructed and form wild-type, black pigment. Melanocyte lines can now be reproducibly generated from mice of different strains, and provide tools for molecular studies of germline coat-colour mutations. These two lines provide elegant means to study the developmentally controlled expression of the two complementary genes, B and C, with black melanin pigment as a readily detectable natural marker.