&NA;DNA extracted from 31 primary colorectal carcinomas was analyzed for the presence ofrasgene amplification and mutations. Nine carcinomas had Ha‐rasamplification and seven Ki‐rasamplification. Nine carcinomas had codon 12 Ki‐rasmutations. Immunohistochemical staining forrasproteins revealed a normal membrane association in normal mucosa and benign polyps but an abnormal cytoplasmic distribution in carcinomas. Amplification, mutations, and immunohistochemical staining were independent of histologic differentiation, Duke's stage, or DNA ploidy status. This study demonstrates that abnormalities ofrasgenes are a common finding in colorectal carcinomas. They are potentially important biologic changes associated with malignancy, although they do not appear to be related to clinical behavior.