Abstract: In the present study, the clinical significance of circulating immune complexes (CIC)and complement is evaluated in fifty-four patients with SLE. In nephritis group, CH₅₀ and C₃ levels were significaatly lower in active stage compared to those in inactive stage, and the degree of reduction of CH₅₀ and C₃ levels was correlated to the disease activity.The mean valuse of CIC were in normal range in both active and inactive stages. In non-nephritis group, CIC by PEGP method was significantyly higher in active stage compared to those in inactive stage, and was parallel to the degree of disease activity. However, the changes in ACA, CH₅₀ and C₃ failed to show any significant differences between the two stages.The results in this study also suggested that an abnormal increase of CIC level by PEGP method might be used for the prediction of the exacerbation of the disease in non-nephritis group.