Overexpression of the p53 gene product has been observed in a high percentage of malignant melanomas. To evaluate the role of this protein in the development of melanoma, we examined p53 expression in benign, premalignant, and malignant melanocytic lesions. Using the antibodies DO-7 and 1801, which recognize both wild-type and most mutant forms of the p53 protein, we analyzed by immunohistochemical staining 26 benign nevi, 34 dysplastic nevi from patients at low risk for the development of melanoma, 22 dysplastic nevi from patients at high risk for the development of melanoma, 61 primary melanomas (including 15 that arose from dysplastic nevi), and 10 metastatic melanomas. Expression of the p53 protein was not observed in any of the benign or dysplastic nevi. Of the primary melanomas only 3 (5%) demonstrated nuclear staining, whereas 70% of the metastatic melanomas showed a positive reaction for p53. These data suggest that overexpression of the p53 gene product is a late event in the progression of melanoma and consequently indicate that expression of this protein cannot be used as a marker to identify patients at high risk for the subsequent development of melanoma.