The effects of oxandrolone on plasma lipids and lipoprotein composition in patients with type IIa, IIb and IV hyperlipoproteinemia were investigated. Oxandrolone (4 mg/day, for 28 days) induced a significant reduction in plasma and VLDL triglyceride. Reciprocal elevation of LDL cholesterol was observed in 8 of 10 type IV patients and in 2 of 5 type IIb patients. In patients with type IV hyperlipoproteinemia, significant reduction of plasma apolipoproteinB and VLDL apolipoprotein B and inverse LDL apolipoprotein B increment was observed after treatment with oxandrolone. HDL cholesterol was decreased. Hypo-high density lipoproteinemia defined as HDL cholesterol concentration below 40 mg/100 ml occurred in 7 of 10 type IV, 3 of 6 type IIb and 1 of 4 type IIa patients.