Serum uric acid, triglycerides, cholesterol, and lipoprotein levels were determined in 35 patients with primary avascular necrosis of the femoral head. The results were compared with a control group and a group of gouty patients. Frequency distribution of the data in the three groups was found to be of the log normal type, and the statistical calculations were performed after log transformation of the serum values. Compared to the control group, a significant increase in the levels of triglycerides, cholesterol, pre-beta-lipoprotein, and uric acid were found in the patients with avascular necrosis. No significant difference was observed between lipid and lipoprotein levels in gout and avascular necrosis, although the serum uric acid was higher in the gouty patients. In contrast to the findings in gout, the uric acid levels did not correlate with the lipid or lipoprotein fractions in patients with avascular necrosis. There were no statistical differences between lipid, lipoprotein and uric acid levels in patients with avascular necrosis receiving corticosteroids or using alcohol, as compared with those not taking these drugs. It is concluded that avascular necrosis of bone complicating longterm use of steroids or alcohol is not induced directly by the two drugs, but that the initiating event may lie in lipid disturbances.