Expression of mutant p53 detected by immunohistochemistry has been described in human malignant melanoma, but there are few reports of molecular analyses. To investigate the genetic basis for p53 expression in malignant melanoma, we examined 58 primary tumors and 5 cutaneous metastases. The entire coding sequence of the p53 gene was screened by single-strand conformation polymorphism analysis and direct genomic sequencing of polymerase chain reaction products. p53 and mdm-2 expression were studied by immunohistochemistry. Two p53 gene mutations could be found in 1/63 samples examined, both having occurred in the same specimen from a patient with a nodular melanoma. p53 and mdm-2 expression were found immunohistochemically to increase with tumor progression both in frequency and in the mean proportion of positive cells, with the same cases staining positively for both antibodies. Our results suggest that a) p53 gene mutations are a rare event in human melanoma; b) accumulation and thus immunohistochemically detectable expression of p53 may result from posttranslational mechanisms affecting the p53 gene product; and c) p53 and mdm-2 are more important in late events in melanoma carcinogenesis.