Alterations in the p53 gene have been described in a variety of human malignant neoplasms. We have examined 29 stage B prostate carcinomas for alterations in the p53 gene and for amplification of the MDM-2 gene. No evidence of mutations in the conserved exons 5 to 8 was found by polymerase chain reaction single-stranded conformation polymorphism analysis and no accumulation of p53 protein was found by immunohistochemistry. However, loss of heterozygosity at the p53 locus was observed in 11% of information cases. Amplification of the MDM-2 gene was not observed by Southern blot hybridization. In contrast, stage C and D prostate carcinomas showed accumulation of p53 protein in 33 to 66% of cases. We conclude that alterations in p53 function are infrequent in clinically localized prostate cancers but are more common in advanced cancers.