Previously we reported that dietary supplemental vitamin B6 (B6) reduced colon tumorigenesis and cell proliferation in mice receiving azoxymethane (AOM) for 22 weeks. This study was conducted to examine the influence of short-term consumption (5 weeks) of diets containing graded levels of B6 and fat on colonic cell proliferation in mice with or without receiving AOM. In experiment 1, mice were fed the 10% corn oil diet containing 1, 7, 14, 35 or 70 mg pyridoxine HCl/kg, and received weekly injections of AOM for the initial 3 weeks. In experiment 2, mice were fed 5 or 20% corn oil diet containing 1, 7, 14 or 35 mg pyridoxine HCl/kg, and received weekly injections of AOM or saline for the initial 3 weeks. In experiment 1, supplemental B6 caused a dose-dependent reduction of colon aberrant crypt foci and cell proliferation (BrdU-labeling index) among the 1-14 mg pyridoxine HCl/kg. There was no influence of B6 on these parameters among 14-70 mg pyridoxine HCl/kg. Immunohistochemical analysis of apoptosis labeling by TUNEL method indicated no influence of dietary B6 on colon apoptosis. In experiment 2, supplemental B6 significantly reduced colon cell proliferation regardless of AOM injection. This inhibitory effect on cell proliferation was markedly enhanced by a high-fat diet, but slightly affected by AOM treatment. The results suggest that dietary supplemental B6 inhibits colon cell proliferation from the early stage of colon carcinogenesis, and a high-fat diet markedly enhances the inhibitory effect.