Reticuloendothelial system Fc receptor function was measured in 10 patients with systemic lupus erythematosus (SLE) taking corticosteroids, 10 SLE patients not receiving corticosteroids and in 19 controls, 9 of whom were corticosteroid-dependent asthmatics and 10 of whom were healthy. Clearance studies were performed using autologous 51 Cr-labeled erythrocytes that had been sensitized with human IgG anti-Rh(D) [6,700 molecules/cell]. The clearance curves could be split into a fast (t1/2 fast) and a slow (t1/2 slow for any of the groups of patients. The results were correlated with serum C3, C4, DNA-binding, fluid phase 125I-Clq binding, a disease activity index, corticosteroid dose and duration of therapy with corticosteroids. The only significant correlation was an inverse correlation of C4 with the t1/2 slow in SLE patients not on corticosteroids (r=- 0.71, p less than 0.05). The t1/2 slow of the 3 SLE patients with active nephritis (86 +/- 40 min) was significantly different from the 17 SLE patients with inactive nephritis or normal renal function (37 +/- 5 min) (P less than 0.05). We conclude that there is no overall defect of Fc receptor function in our patients with SLE although there is decreased clearance in patients with active lupus nephritis.