We have screened for mutations in the Cip1/Waf1 gene using Southern blot analysis and the polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) method in diverse human tumors. Seven of 102 (7%) human tumor samples were identified to have point mutations within the coding region of the Cip1/Waf1 gene. Two of the seven mutated cases showed gene rearrangements. These results suggest that the frequency of genetic alterations in the Cip1/Waf1 gene is relatively low in comparison with several known tumor suppressor genes.