ABSTRACTCirculating immune complexes were detected by the polyethylene glycol precipitation method in the sera of patients with antibodies to ribonucleoprotein (RNP). Levels of immune complexes were significantly higher than in normal control sera and correlated well with disease activity as defined by clinical manifestations, decreased levels of complement and increased fluorescent anti‐nuclear antibody titers.Analysis of IgG‐aggregates in the sera of patients revealed the following characteristics: molecular weight of about 900,000 daltons, sensitivity to RNase, resistance to DNase, no Clq‐binding activity and no RF act