Forty subjects (20 male, 20 female) ages 50 or older, with LDL cholesterol concentrations greater than 130 mg/dl were fed each of five diets for eight week periods. The baseline diet consisted of 36 percent of energy as fat (15 percent saturated, 15 percent monosaturated, 6 percent polyunsaturated) and 160 mg cholesterol/1000 kcal. The experimental diets contained 30 percent energy as fat, 2/3 of which was derived from each of the following: 1) unhydrogenated liquid soybean oil, 2) soybean oil margarine in tub form, 3) commercial shortening, and 4) butter in a randomized double blind, cross-over design. With the exception of the experimental fat, all other foods in the reduced fat diets were identical.