Neutrophil chemotaxis, random motility, serum chemotactic activity derived from complement activation by classical or alternative pathways, and the presence of serum inhibitors of chemotaxis were all studied in 24 patients affected by Systemic Lupus Erythematosus (SLE) and in an equal number of healthy control subjects. Statistical comparison between patients and controls indicated lower chemotactic activity in patient's serum when activated by the classical pathway, and the presence in some SLE patients of a heat-labile inhibitor of the chemoattractants. Low "classical pathway" chemotactic indexes were correlated with low C4 values, active nephritis and recurrent infections. The presence of heat-labile inhibitor was correlated with low values of C3. Our data suggest that defective neutrophil chemotaxis could be one of the mechanisms contributing to the high incidence of infections suffered by SLE patients. The importance of conducting separate studies on cell movement and on generation of serum chemotactic activities by classical and alternative pathways in SLE patients is discussed.