In the present study, we analyzed human ovarian carcinoma cell lines for abnormalities in the tumor suppressor gene Rb (retinoblastoma) and in cyclin-dependent kinase 4 (CDK4) inhibitor genes (p16^INK4and p15^INK4B) using molecular biology techniques. For the Rb gene, in all six cell lines (PA-1, Caov-3 and -4, OVCAR-3, SK-OV-3, and Kuramochi), Rb gene abnormality was not detected using Southern blotting. In the Caov-3 cell line transcripts were not detectable by either Northern blot or polymerase chain reaction. Sequence analysis of the entire coding region of the Rb gene revealed point mutations (AAC to GAC) resulting in codon 123 (Asn to Asp) changes in the Caov-4 cell line. In the PA-1 cell line both wild-type Rb and mutant-type Rb (codon 798: CGG to TGG) were expressed, and in the OVCAR-3 cell line both wild-type Rb and mutant-type Rb (codon 704: ATG to GTG) were expressed. In four of six human ovarian carcinoma cell lines Rb gene abnormality was detected. For the p16^INK4and p15^INK4Bgenes, only the SK-OV-3 cell line had abnormalities. There was a gene rearrangement or minor deletion of the p16^INK4gene in the SK-OV-3 cell line, while the p15^INK4Bgene was deleted in this cell line. In the SK-OV-3 cell line no mRNAs of p16^INK4and p15^INK4Bwere expressed. At the point of Rb gene inactivation, we can explain five cell lines of six: four cell lines had abnormalities in the Rb gene itself, which is another mechanism by which the Rb gene is inactivated, while one cell line (SK-OV-3) had abnormalities in CDK4 inhibitor genes, another of the inactivation mechanisms of the Rb gene. These data suggest that abnormalities of Rb and CDK4 inhibitor genes (p16^INK4, p15^INK4B) may be involved in human ovarian carcinogenesis.