Concentrations of interleukin-2 receptors were studied in sera of 81 patients with pauciarticular-, polyarticular-, and systemic-onset juvenile chronic arthritis using a double antibody "sandwich" enzyme-linked immunosorbent technique. Serum concentrations were significantly increased in all subgroups when compared with the healthy controls. Higher concentrations were found in systemic onset disease than in pauci- or polyarticular onset disease. Serum levels were found to be increased in both inactive and active disease, showing maximal values in patients with systemic features. A correlation to C-reactive protein, alpha 1-acid glycoprotein, and erythrocyte sedimentation was observed. Increased sIL-2R values suggest disease activity despite the absence of clinical symptoms.