Positive tests for antinuclear antibodies (ANA) were found in 51 of 58 (88%) patients with chronic iridocyclitis and juvenile rheumatoid arthritis (Still's disease). Antinuclear antibodies were predominantly of the IgG class of immunoglobulins and were generally present in liters of 1:50 (six ANA units) or more. They were unassociated with disease activity, severity or duration, age of patient at onset or testing, or sex. Neither other autoantibodies nor antibodies reactive with DNA or RNA were associated. In 8 patients tested early in disease, ANA were found prior to the onset of iridocyclitis. The presence of ANA should prove useful in identifying patients with JRA at risk for chronic iridocyclitis. In contrast, negative tests for ANA in patients with childhood-onset arthritis and iridocyclitis were found to be associated with acute iridocyclitis and subsequent ankylosing spondylitis.