Cellular transforming genes can be detected in human tumours by DNA-mediated transfection into NIH 3T3 mouse fibroblasts. The activated transforming genes have been, in most cases, members of the ras gene family, of which the most frequently found is the c-Ki-ras oncogene and least frequently the c-Ha-ras gene. An increasing number of studies has identified the presence of activated N-ras (which has no known viral homologue) in human tumour cell lines. Furthermore, other transforming genes, distinct from the ras gene family, have been reported in B-and T-cell lymphomas. The activation of c-Ha-ras and N-ras has been described in some cell lines derived from cases of human malignant melanoma. Here we describe the presence of transforming activity in the DNA from a human melanoma cell line which shows weak homology with members of the ras oncogene family.