Abstract Novel cell lines, designated NM78-AM and NM78-MM, have been established from a malignant melanoma of the cheek oral mucosa. NM78-AM cells were spherical, grew in suspension as clusters, and produced no melanin. In contrast, NM78-MM cells were adherent and produced melanin granules. Initially, NM78-AM cells were grown on fibroblast feeder cells or in growth media supplemented with 10% conditioned medium from fibroblasts, but eventually grew in standard growth media alone. NM78-AM cells had interdigitating microvilli and formed cell clusters. They had large nucleoli, desmosomes, lipid droplets, and well-developed Golgi apparatuses. In contrast, NM78-MM cells grew as adherent neuron-like cells. They had large prominent nucleoli, irregular nuclear membranes, a number of mitochondria, well-developed Golgi apparatuses, melanosomes at various stages of development in the cytoplasm, and the cells secreted melanin granules. Projections from these melanotic cells formed anastomoses with each other. NM78-MM cells stained immunofluorescently for internexin, neuron specific enolase, NF-200, and glial fibrillary acidic protein. These cells were severely aneuploid, approximating to triploidy, and had many marker chromosomes. We used a real-time monitoring system to evaluate oxygen concentrations in culture medium to investigate the susceptibility of both cell lines to various anti-cancer drugs. NM78-AM cells were slightly sensitive to actinomycin D, but not to cisplatin, irinotecan, the irinotecan metabolite SN-38, taxol, taxotere, bleomycin and methotrexate; NM78-MM cells were sensitive to cisplatin, and not to taxol, taxotere, carboplatin, and irinotecan. These new cell lines, NM78-AM and NM78-MM, will be very important for the development of new chemotherapeutics for oral malignant melanoma.