Twenty children with juvenile chronic arthritis (JCA) and two children with SLE were investigated as to the existence of immune complexes in a long-term survey over 24 months. Two different methods were applied, a solid phase C1q RIA and a polyethylene glycol precipitation test. Detection of immune complexes was compared to the course of the disease and other laboratory data. C1q RIA showed a distinctly higher number of positive tests than the PEG precipitation test. The presence of immune complexes appears to be transitory in the course of JCA, as was demonstrated by C1q RIA. A connection with a more advanced stage of the disease is postulated. The positive test can be regarded as a prognostic parameter which, however, cannot be used for the diagnosis of JCA.