The p53 gene on chromosome 17p is considered to be a tumor suppressor gene, and frequent mutations of the p53 gene have been found in a wide variety of human cancers. We examined 31 ovarian cancers for allelic losses and mutations of the p53 gene by polymerase chain reaction-single strand conformation polymorphism analysis as well as restriction fragment length polymorphism analysis. Allelic loss of the p53 gene was detected in 16 of 20 cases (80%). Mutations were detected in 9 of 31 cases (29%): 2 cases in exon 4; 5 cases in exons 5-6; and 2 cases in exons 7-8. In 8 of 9 cases, p53 mutations were accompanied by losses of the normal allele. These alterations of the p53 gene were commonly detected from stage I to stage IV. These results suggest that alterations of the p53 gene play an important role in the development of human ovarian cancers.