Circulating immune complexes (CIC) have been described in the hemolytic uremic syndrome (HUS) in children. They may represent an epiphenomenon or could be related to the platelet activation and endothelial damage observed in this disease. In an attempt to define this relationship, we investigated the CIC isolated in 17 patients with the classic form of HUS, by means of monoclonal antibodies against platelet surface glycoprotein lb and IIb–IIIa complex. The negative results obtained do not support the possibility of platelet antigens being constituents of CIC and make an antibody-induced platelet activation in HUS very unlikel