Activity of the lipoprotein lipase (LPL, postheparin lipolytic activity, PHLA) was measured in 50 patients with systemic lupus erythematosus (SLE). The LPL activity was determined by the difference of free fatty acid (FFA) released from incubated substrate (Ediol) and postheparin plasma. Hyperlipidemia except for FFA was observed in almost all of the SLE patients, and was correlated with grade of proteinuria. The LPL activity was significantly decreased in 47 cases. And marked decrease of the activity was observed in cases of the active phase. The LPL activity was not correlated with levels of serum lipids. The LPL activity of cases, which were accompanied by nephrotic type of lupus nephritis or elevated blood urea nitrogen, showed almost the same as the mean value of total 50 cases. Also the LPL activity was decreased even in patients who had been not received steroid treatment. It is reasonably presumed that SLE is a disorder which demonstrates depression of the LPL activity.