Circulating immune complexes were demonstrated in about 50% sera of 70 patients with Hodgkin's disease. Circulating immune complexes were detected by using two methods. The inhibition of RF Latex agglutination detects those immune complexes which contain immunoglobulins G as antibodies. Another test applied in this work is based on the selective precipitation of soluble immune complexes by 3g% solution of polyethylene glycol (PEG). This test is suitable for further characterisation of immune complex constituents. Analyses of PEG precipitates obtained after adding PEG to sera of patients with Hodgkin's disease showed that immunoglobulin G were present in all analysed cases. In some analysed PEG precipitates beta-lipoproteins were also identified among precipitated proteins. The obtained results, therefore, suggest the possibility that detected complexes are not obviously immune complexes, but the serum protein complexes of some other type.