Abstract.Clinical significance of immune complex‐like material in the serum was investigated in tumour patients undergoing plasma exchange with albuminsaline solution and subsequent chemotherapy. Immune complexes were detected by the C1q binding assay or the Raji cell radioimmunoassay in nine out of forty‐five patients before this therapy.Levels of immune complexes were decreased to 10–30% of the initial value by plasma exchange depending on exchanged plasma volume. In contrast to other serumproteins likeα1‐antitrypsin andα2‐macroglobulin, which showed protein specific increase during follow up after plasma exchange in all patients, recovery rates of immune complexes and IgG were highly individual but parallel in each patient.Clinical response to this protocol did not correlate with immune complex status, suggesting that removal of the measured immune complex like material had little clinical significance or was not longlasting enough to provide therapeu