The effects of guar gum and wheat bran on blood and liver lipid levels of rats were measured. In experiment 1, rats were fed ad libitum a 55% sucrose diet containing 0, 15 or 25% wheat bran for 3 weeks. Postprandial plasma triglyceride, liver triglyceride and liver cholesterol values in rats fed the sucrose diet with wheat bran were significantly lower than values for rats fed the diet without wheat bran. Neither fasting plasma triglyceride nor cholesterol values were altered by wheat bran. In experiment 2, rats were meal-fed one of four experimental diets for 3 weeks: sucrose, sucrose-cholesterol, sucrose-cholesterol-bran or sucrose-cholesterol-guar gum. Rats fed sucrose-cholesterol-guar gum diet had significantly lower fasting plasma total cholesterol, liver triglyceride and liver cholesterol values, but higher plasma high density lipoprotein (HDL) cholesterol values than those fed sucrose-cholesterol diet. These values were similar for the sucrose-cholesterol and sucrose-cholesterol-bran groups. Fasting plasma triglyceride levels were not altered by wheat bran or guar gum. These studies indicate that while guar gum lowers fasting plasma total cholesterol and raises HDL cholesterol, wheat bran does not.