Psyllium hydrophilic mucilloid was examined for its ability to lower serum cholesterol levels in hypercholesterolemic patients. Seventy-five patients with mild to moderate hypercholesterolemia were evaluated in this randomized, double-blind, placebo-controlled parallel study. Patients were treated with a Step I diet for 12 weeks before receiving placebo or 3.4 g of psyllium (equivalent to 1 teaspoon) three times per day for 8 weeks. Compared with placebo, psyllium achieved an additional 4.8% reduction in total cholesterol level, 8.2% reduction in low-density lipoprotein cholesterol level, and 8.8% reduction in apolipoprotein B level. Psyllium did not significantly affect blood pressure or levels of high-density cholesterol, triglycerides, serum glucose, or iron. Reported adherence to diet and treatment was excellent, and no significant adverse side effects were noted. These results indicate psyllium hydrophilic mucilloid is an effective and well-tolerated adjunct to diet in the management of mild to moderate hypercholesterolemia.