Fully refined, bleached, deodorized corn oil and soy oil, and lightly hydrogenated, winterized soy oil were compared for effectiveness in lowering plasma cholesterol. Twenty-four, healthy, young college students were the subjects for the 10-wk studies. At the 300 cal level, the corn oil and unhydrogenated soy oil diets contained approximately 53 g of polyunsaturated and 26 g of saturated fat. The hydrogenated soy oil diet contained 42 and 25 g, respectively. All diets contained approximately 700 mg of cholesterol. Corn oil and unhydrogenated soy oil were equally effective in lowering both total and low density lipoprotein cholesterol. Lightly hydrogenated soy oil was also quite effective, but less so that the more unsaturated oils. Triglycerides were also lowered, but very low density and high density lipoprotein cholesterol concentrations, as well as total high density lipoproteins, were scarcely affected. All of the polyunsaturated fat diets produced small but statistically significant reductions in the cholesterol to protein ratio of all three lipoproteins.