In an effort to analyze molecular mechanisms of human ovarian carcinogenesis, we studied the structure and expression of the p53 gene in different cell lines established from human ovarian carcinomas. In all six lines (PA-1, Caov-3 and -4, OVCAR-3, SK-OV-3, and Kuramochi), p53 abnormalities were detected. In the SK-OV-3 cell line, Southern analysis suggested the presence of sequence deletions/rearrangements in at least one allele of the p53 gene, and transcripts were not detectable by either Northern or polymerase chain reaction analysis. Sequence analysis of the entire coding region of the p53 gene revealed point mutations resulting in codon changes of a highly conserved region of the protein in four cell lines, Caov-3 and -4, OVCAR-3, and Kuramochi. In the Caov-3 cell line, the point mutation resulted in chain termination at codon 136. Quantitation of p53 protein by immunoprecipitation analysis revealed a 6-fold higher than control cell level in PA-1. By contrast, p53 protein was not detectable in lines Caov-3 and SK-OV-3. We conclude that altered levels of p53 gene expression and/or mutant forms of the p53 gene product are associated with all human ovarian cancer cells tested.