The comparative effects of 10 different dietary fibers on serum and liver lipids were investigated by feeding male Sprague-Dawley rats diets containing 10 g cholesterol + 2 g cholic acid/kg diet, with 60 g fiber/kg diet. Diets were fed for 3 wk; cellulose was the control fiber. Rats fed psyllium (rich in soluble fiber) had the lowest serum and liver cholesterol concentrations. Rats fed other soluble fiber-rich fibers (oat gum, guar gum and pectin) also had significantly lower serum and liver cholesterol concentrations than rats fed cellulose. Although feeding diets containing both soluble and insoluble fibers (soybean fiber and oat bran) did not significantly alter serum cholesterol, liver cholesterol values were significantly lower than those of cellulose-fed rats. Rats fed rice bran, predominantly an insoluble fiber source, had significantly higher liver cholesterol and significantly lower body weight gains and serum triglyceride concentrations than cellulose-fed rats. Values for serum and liver cholesterol were similar for rats were fed insoluble-rich fibers (corn bran, cellulose and wheat bran). These observations indicate that feeding dietary fibers rich in soluble fiber produces lower serum and liver cholesterol concentrations than does feeding commonly available sources of water-insoluble fiber.