The effect of cholecystectomy on colon carcinogenesis induced by methylazoxymethanol (MAM) acetate was examined in four groups of Syrian golden hamsters. For the sexes combined, the incidences of total large intestinal neoplasms and adenomas in Group 1, which received cholecystectomy and a single intravenous injection of MAM acetate (20 mg/kg body weight), were significantly higher than those of hamsters in Group 2, which were given MAM acetate alone. The combined multiplicities of total large intestinal neoplasms from male and female hamsters, and the multiplicities of those in females of Group 1 were also significantly higher than those in animals in Group 2, respectively. No intestinal tumors were observed in hamsters in Group 3 (cholecystectomy alone) or Group 4 (untreated control). These results indicate an enhancing effect of cholecystectomy on MAM acetate-induced large intestinal carcinogenesis in hamsters.