Non-familial human adrenocortical adenomas and carcinomas were screened for mutations in exons 5-8 of the p53 tumor suppressor gene by single-strand-conformation-polymorphism (SSCP) analysis, followed by direct sequencing of PCR-amplified DNA. Point mutations in codons 12, 13 and 61 in H-ras, K-ras and N-ras proto-oncogenes were similarly assessed by direct DNA sequencing. Three out of 15 primary adrenocortical carcinomas (20%) contained a mis-sense point mutation in the conserved regions (exons 5 and 8) of the p53 gene. Mutations were located in codon 157 (GTC-->TTC; Val-->Phe), codon 163 (TAC-->AAC; Tyr-->Asn), and codon 273 (CGT-->TGT; Arg-->Cys). The mutation in codon 157 was detected in the primary tumor as well as in brain and lymph-node metastases. Among 18 adrenocortical adenomas, there was only a single non-miscoding mutation in codon 295 (CCT-->CCC; Pro-->Pro). These data suggest that mutational inactivation of the p53 gene occurs in a minority (20%) of sporadic adrenocortical carcinomas and that these mutations constitute a late event in the multi-step process of malignant transformation. No ras mutations were detected in any of these tumors, suggesting that these genes are not involved in the development of tumors originating from the adrenal cortex.