The effect of immune complexes (IC) isolated from systemic lupus erythematosus (SLE) sera with polyethylene glycol and gel filtration on the chemotaxis and Fc receptor function of healthy monocytes was examined. Even at a low protein concentration (1 microgram/ml = 1 mg/l) ICs inhibit monocyte chemotaxis. ICs from patients with SLE nephritis are more inhibitory than ICs from patients without renal disease. The inhibitory effects of ICs on monocyte chemotaxis and Fc receptor activity are similar, suggesting a relationship between the chemotactic and Fc receptor function of monocytes. Analysis of the ICs by enzyme-linked immunoassay showed no correlation between the quantity of IgG, C3, and anti-DNA in the IC samples and their effects on monocyte function.