Two prostate carcinoma cell lines, DU-145 and PC-3, were examined for abnormalities in the retinoblastoma (Rb) and the p53 putative tumor suppressor genes. We found an abnormal Rb gene product in DU-145 using Western blot analysis. Polymerase chain reaction amplification followed by direct DNA sequencing demonstrated a base substitution mutation that generates a stop codon in exon 21. On Northern, Southern, and Western blot analysis, the p53 gene and its product appear to be normal in DU-145. PC-3, however, failed to demonstrate expression of either the p53 transcript on Northern blot analysis or the p53 protein on Western blot analysis, while the Rb gene products appeared to be normal on both Northern and Western blot analysis. This work extends the correlation between abnormal expression of putative tumor suppressor genes and human malignancies.