The effect of diets with various dietary fiber sources on the plasma lipids, liver cholesterol, the histology of the gastrointestinal tract, heart, liver and kidney and the fecal neutral steroid excretion was investigated in hamsters. 155, 9-11 wk old, male Golden-syrian hamsters were fed a purified basal hypercholesterolemic diet (0.1% cholesterol, 10% fat, 4% dietary fiber) for 5 wk to elevate plasma lipid levels. Based on wk 4 plasma total cholesterol (TC) levels hamsters with elevated levels were randomly assigned, 16 animals/group, into six groups for another 4 wk: control, oat bran, guar gum, cellulose, xylan and sacrifice. After 4 wk of the fiber diets (10% dietary fiber), the plasma TC levels were significantly lowered in the oat bran, guar gum and xylan groups (16%, 12% and 15%, respectively) (p<.05). They were also significantly lower than the control and cellulose groups. Plasma HDL-C concentrations tended to be lower in all the treatment groups, but was significantly decreased only in the guar gum group (12%) (p<.05). The combined plasma VLDL-C + LDL-C was significantly lowered by the oat bran, cellulose and xylan diets (38%, 40% and 34%, respectively) (p<.05). The liver cholesterol concentration increased significantly from 1 mg cholesterol/g liver to 4.1 mg cholesterol/g liver (p<.05) after 4 wk of the control diet; this was further increased significantly only in the cellulose group (5.6 mg cholesterol/g liver), while the other treatment groups showed no significant changes or differences compared to the control diet group (wk 4). The total fecal neutral steroid excretion was significantly (p<.05) higher in the oat bran group compared to the other treatment groups. No major differences were observed in the tissue histology of the animals in the different treatment groups. In the present study, it appeared that oat bran, guar gum and xylan were effective hypocholesterolemic agents; however, their mechanism of action is still not clear.