Proliferation of T and CD4 cells in the autologous mixed lymphocyte reaction (AMLR) was determined for children with juvenile rheumatoid arthritis (JRA) and children with other rheumatic and connective tissue diseases. Children with musculoskeletal symptoms but no rheumatic disease and healthy adults served as controls. Patients with polyarticular rheumatoid factor (RF) positive JRA had a diminished CD4/non-T cell AMLR, whereas those with RF negative polyarticular and pauciarticular onsets had normal results.