The effect of guar gum (15 g/day) on serum lipids and body weight of middle-aged hypercholesterolemic females was studied in a double-blind controlled trial. No consistent changes were observed in serum cholesterol, triglycerides or HDL cholesterol in patients taking guar gum, placebo or no medication at all. A highly significant decrease in body weight (62.9 +/- 2.1 vs. 60.4 +/- 2.2 kg, p < 0.0005, paired comparison) was seen in subjects receiving guar gum, whereas body weight remained constant in the other two groups. It is concluded that the daily ingestion of 15 g of guar gum results in a permanent weight loss, but does not influence serum lipids in females with hypercholesterolemia.