Monocytes from 11 patients with rheumatoid arthritis and 10 control subjects were purified by countercurrent elutriation. Rheumatoid arthritis monocytes had more cell-associated IgG (P less than 0.001) and bound more 125I-labeled heat-aggregated IgG in vitro (P less than 0.02) than did monocytes from control subjects. Interaction of rheumatoid factor (RF) with monocytes was then investigated. Purified 125I-labeled IgM-RF and IgG-RF bound directly to monocytes from normal individuals. Furthermore, preincubation of normal monocytes with RF augmented subsequent binding of aggregated IgG to the cells. We conclude that monocyte-associated RF can enhance binding of IgG-containing immune complexes to the cells and can exaggerate the measured number of Fc receptors. Such cell-bound RF may affect clearance of immune complexes by the reticuloendothelial system in vivo.