The genetic changes of cyclin A, DI, E and CDK2 were examined in human colorectal carcinomas by Southern-blot analysis. Gene amplification of cyclin E was detected in 5 of 53 (9.4%) primary colorectal carcinoma tissues. Interestingly, in 3 of 5 tumors showing cyclin E gene amplification, the CDK2 gene was amplified simultaneously with rearrangements. No obvious correlation was detected between gene amplification and clinicopathological features of colorectal carcinomas. Out of 7 colon carcinoma cell lines, 2 showed gene amplification of cyclin E without gene amplification of CDK2. No amplification of cyclin A or DI gene was found in any of the colorectal carcinoma tissues or colon carcinoma cell lines. Our results suggest that the concurrent amplification of cyclin E and CDK2 genes may play a role in colorectal carcinogenesis.