[en] A new technique for the detection of glycoprotein antigens in immune complexes (IC) isolated from serum is described. The technique was developed with a model IC system consisting of ovalbumin (OVA)-rabbit anti-ovalbumin antibodies (aOVA), at 3 times antigen excess. OVA-aOVA IC added to normal human serum (NHS) were purified by absorption onto and elution from tubes coated with rheumatoid factor (RF) and were subjected to electrophoresis in polyacrylamide gels. Concanavalin A (Con A)-binding proteins were detected by treating the gels with radioiodinated Con A (¹²⁵Con A), followed by autoradiography. IC isolated from sera of patients with Burkitt's lymphoma (BL) and Nasopharyngeal Carcinoma (NPC) were analysed before and after reduction with dithiothreitol. TWo closely spaced proteins of about 40 kdalton were identified in the reduced samples in 26 of 30 BL sera (86%) and in 24 of 30 NPC sera (80%) but were not seen in 30 sera of African patients with a variety of unrelated tumours nor in 12 sera of European blood bank donors. (Auth.)