The uptake of 125I-heat aggregated human IgG (125I-HAGG) by monocyte-free peripheral blood lymphocytes was investigated in patients with active rheumatoid arthritis (RA), inactive RA patients with other inflammatory joint diseases (ankylosing spondylitis and Still's disease), and in normal controls. The lymphocytes of patients with RA, whether active or inactive, showed significantly raised levels of 125I-HAGG uptake when compared with normals. Patients with other inflammatory joint diseases showed normal levels of HAGG uptake. High uptake was not due to the presence of cytophilic antibodies and was not related to drug treatment, rheumatoid factor status, patient age, duration of disease, and did not correlate with disease activity. These results indicate that Fc-receptor bearing lymphocytes in patients with RA differ from those of normal subjects and patients with other inflammatory joint diseases. This difference was not due to differences in numbers of Fc-receptor bearing lymphocytes but may be due either to increased numbers of Fc-receptors on each cell or to increased avidity of such receptors for HAGG.