The dietary pattern and fecal constituents of two populations with distinct risk for the development of colon cancer, a high-risk population in New York Metropolitan area and a low-risk population in rural Kuopio, were studied. The average daily intake of dietary fat and protein was the same in the two groups, but the sources of fat were different, a greater portion coming from dairy products in rural Kuopio and from meat in the New York Metropolitan area. Not only the frequency of bowel movements was higher, but also the daily total stool output as well as the fecal fiber excretion were greater in Kuopio compared with New York due to high dietary intake in rural Kuopio of cereal products rich in fiber. The concentration of fecal secondary bile acids and bacterial beta-glucuronidase activity was lower in rural Kuopio, but the total daily excretion of these constituents was the same in two populations. The daily fecal excretion of bacterial nuclear dehydrogenase activity and of neutral sterols was higher in rural Kuopio, and the concentration of these constituents was the same in the two groups. The high daily excretion of cholesterol metabolites in Kuopio might be due to high dietary intake of dairy products. The data suggest that one of the factors contributing to the low-risk of large bowel cancer in Finland, in spite of high dietary intake of fat, appears to be the fact that a high dietary fiber leads to an increase in stool bulk, thus diluting bile acids, which have promoting activity.