Three primary and 16 metastatic melanoma cell lines were established from primary and metastatic lesions of 4 patients with malignant melanoma. Comparison of metastatic melanoma cells with cells of the vertical growth phase (VGP) or late primary melanoma from the same individual revealed, generally, a shorter population-doubling time, growth to a higher cell density, higher tyrosinase activity, and more pigmentation in metastatic cells. Conversely, primary and metastatic melanoma cells had similar morphology, plating efficiency, and tumorigenicity in nude mice. Karyotypic analysis revealed clonality and nonrandom abnormalities in chromosomes 1, 6, and 7 in cells of the primary and metastatic lesions of the 3 patients studied. Few differences were found in the expression of melanoma-associated antigens on short-term and long-term cultured cells by tests with monoclonal antibodies in mixed hemadsorption assays, flow cytometry, and radioimmunoassays. Our results indicate that cells cultured from the VGP but not from the radial growth phase of primary melanoma are similar to metastatic melanoma cells.