The expressions of cyclins A, D1 and E at the protein level were investigated by Western blotting in human colorectal carcinomas and in adjacent non-neoplastic colorectal mucosas. Cyclin E was higher in the cancer tissue than in the non-neoplastic mucosa in 92% patients (35 out of 38 cases). However, the cyclin A expression of the mucosa was higher than that of the cancer tissue in 63% (25 out of 40 cases) cases, and only 4 (10%) cancers had higher cyclin A expression. Eleven cancers (27%) demonstrated expression equivalent to that in the mucosa. Equal expression of cyclin D1 in cancer and mucosal tissues was found in 51% cases (20/39), lower expression of cyclin D1 by cancer tissues was demonstrated in 41% cases (16/39) and only three cancers showed higher expression than the mucosa. Proliferating-cell nuclear antigen immunohistochemistry revealed that the labeling index of the cancer tissue was 43.5 +/- 8.3% while that of the mucosa was only 14.8 +/- 5.1%. These results proved that colorectal cancers express high levels of cyclin E, consistent with a high rate of cell proliferation, whereas most of such cancer lose control of cyclin A and cyclin D1 expression.