Although oncogenically activated ras alleles are common in some types of human cancers, the frequency in human carcinoma of the prostate (CaP) has not previously been addressed. In this paper, we report a comprehensive screening of 19 CaPs and 3 CaP cell lines for activating point mutations in the sequences of the 12th and 61st codons of c-Ha-ras-1 and the c-Ki-ras-2 genes, as well as the 12th, 13th, and 61st codons of the c-N-ras gene. The 19 CaPs were chosen to represent a wide range of stages (B through D), Gleason scores (3 through 10), and DNA ploidy (diploid with low proliferation to nontetraploid-aneuploid). Fifteen of the tumors had been untreated prior to resection and 4 were obtained postradiation therapy. The polymerase chain reaction was used to amplify genomic DNA sequences and transcribed mRNA sequences of the ras genes prior to allele-specific oligonucleotide probe hybridization. We have detected a mutant allele with a point mutation in the second nucleotide of the 61st codon of the c-Ha-ras-1 gene in one specimen. Thus, we conclude that the activation of ras alleles is not significant in the development or progression of most CaPs.