Transgenic mice deficient for the p53 gene were reported to frequently develop angiosarcoma (AS), suggesting that alterations in the gene are associated with tumorigenesis of AS. However, little is known about genetic changes, including p53 gene alterations, in human AS because of its rarity. We analyzed p53 mutations on paraffin-embedded specimens from 33 patients with AS by polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) followed by direct sequencing. Age of patients ranged from 18 to 91 (median 70) years, with a male to female ratio of 1.5:1. Sites of tumor were the head in 13 patients, the trunk in 4, the extremities in 4, the heart in 4, bones in 2 and others in 6. PCR-SSCP revealed aberrant mobility shifts of bands in 17 cases: 11 in exon 5, 5 in exon 7 and 4 in exon 8. Direct sequencing on these 17 cases revealed a total of 20 mutations. The frequency of p53 mutations was different by site of tumors: 7 of 13 in head, all 4 in extremities, 2 of 4 in heart and none of 4 in trunk. Our findings suggest that occurrence of p53 mutation is a major pathway for development of human AS.