Effects of environmental carcinogens on DNA can be detected, because, while each carcinogenic agent is inherently different, its corresponding "fingerprint" is unique to a specific mutation pattern. The p53 tumor suppressor gene is of particular interest because the relationship between environmental factors and genetic alterations of carcinogenesis can be investigated. In this report, we compared the mutation patterns of the p53 gene in human colorectal tumors from Japanese patients with those from US patients. The results show different rates of transversion and transition among these two populations, which suggests a difference between Japan and the US in the etiological factors underlying colorectal tumorigenesis.