Effectiveness of a simultaneous inhibition of cholesterol absorption and synthesis, caused by sitostanol ester margarine and pravastatin, was studied to control mild hypercholesterolemia in men with non-insulin-dependent diabetes mellitus (NIDDM) (n = 8). Margarine, 24 g daily, was a basal dietary treatment. Four 7-week intervention periods included margarine, sitostanol (3 g/day) ester margarine, pravastatin (40 mg/day), and sitostanol ester margarine plus pravastatin in a random order. Pravastatin lowered serum total (-32%) and LDL cholesterol (-38%) and apolipoprotein B (-39%) because of enhanced removal (+20%) and decreased production (-26%) of LDL apolipoprotein B, and reduced synthesis (-9%) and turnover (-8%) of cholesterol, which resulted in reduced biliary cholesterol seretion (-18%). Even though serum triglycerides were lowered by 28%, VLDL, IDL, and light and dense LDL became triglyceride-enriched. Despite increasing cholesterol synthesis, sitostanol lowered LDL cholesterol (-14%) by inhibiting cholesterol absorption (-68%) and LDL apolipoprotein B production rate (-20%). Combination of pravastatin and sitostanol ester lowered serum total, VLDL, IDL, and LDL cholesterol and LDL apolipoprotein B by the highest rate, 35%, 50%, 35%, 44%, and 45% from the control margarine period, respectively, because of reduced apolipoprotein B transport rate (but unchanged removal), in both the total and dense LDL subfractions. HDL cholesterol and apolipoprotein A-I kinetics were unchanged. In spite of decreased absorption, cholesterol synthesis was not compensatorily increased. In conclusion, simultaneous inhibition of cholesterol absorption and synthesis lowers LDL cholesterol and apolipoprotein B by 44-45% solely through inhibition of LDL apolipoprotein B production rate in hypercholesterolemic NIDDM patients. A combination of statin to sitostanol ester margarine-resistant patients offers a safe and effective measure to normalize abnormally high cholesterol values, probably with a lowered statin dose.