A total of 120 eight-week-old male rats were exposed to azoxymethane (15 mg/kg body wt in saline s.c.) on Days 1, 4, and 8. Two days after the last injection of carcinogen, the rats were randomized into four experimental groups: two groups were given a chow high in corn oil (23% corn oil) and two groups a chow high in coconut oil (21% coconut oil and 2% corn oil). One group on each chow was kept sedentary, and one group was exposed to moderate exercise, running 2 km/day on weekdays for 38 weeks. At the end of the experiment, the exercising and sedentary rats fed coconut oil were significantly heavier than those fed corn oil. Among the rats fed the high-fat corn oil diet, exercise reduced the number of animals developing carcinomas in the colon (sedentary, 10; exercise, 0) and in the small intestine (sedentary, 5; exercise, 0). The same tendency was observed in the rats fed the coconut oil diet: colon (sedentary, 6; exercise, 3) and small intestine (sedentary, 3; exercise, 2). In the sedentary rats fed the high corn oil diet, 16 intestinal carcinomas were recorded; none were found in the exercised group. In the rats fed the high coconut oil diet, nine carcinomas were recorded in the sedentary groups as opposed to five in the exercised rats. Rats fed the high-fat coconut oil developed significantly fewer neoplasms than the rats fed the equally high-fat corn oil diet.