Eleven human melanoma cell lines with different metastatic ability (both spontaneous and experimental) in nude mice, were analyzed for p53 mutations. Mutations in the conserved regions of the p53 gene were identified by single- strand conformation polymorphism analysis of exons 5-9 and were verified by direct DNA sequencing of polymerase chain reaction products. A mutation was detected in only one low metastatic melanoma cell line with a C→G transition at codon 278, resulting in a substitution of arginine for proline. Only this cell line reacted immunohistochemically with mouse monoclonal antibody PAb 1801, which is immunoreactive with human p53 protein. Another cell line with low metastatic potential showed loss of heterozygosity for p53 with the remaining allele being normal. No mutations were detected in the highly metastatic melanoma cell lines. We conclude that p53 mutations are infrequent in human melanomas and are not a prerequisite for the acquisition of the metastatic phenotype.