The purpose of the present study was to examine the expression of p53 protein in malignant melanomas of the nodular sub-type, with special reference to the role of p53 alterations in the development of metastases. Increased expression of p53 protein was found in 29 of 30 cases using PAb1801 monoclonal antibody (MAb) and flow-cytometric detection on archival material. A large proportion of the cells were positive in a majority of the cases. The level of expression was not correlated to DNA ploidy or to subsequent development of local metastases. However, a significant decrease in p53 protein expression was observed in metastatic lesions, as compared with the corresponding primary tumors. Our results indicate that p53 alterations may be an early event in melanoma development, since almost all cases were affected, and that metastatic spread appears to be parallelled by decreased p53 protein expression.