The authors analyse the value of research into and identification of immune complexes (IC) in chronic inflammatory rheumatisms (CIR) and in rheumatoid polyarthritis (RP) in 93 patients hospitalise in a Rheumatology Department. Comparative levels of ICs were established simple and quick technique of measuring the 50% haemolytic complement (HC 50) used up by the ICs. The rheumatoid factor (RF) is identified at the PEG IC precipitates with the Waaler-Rose test. The existence of raised levels of IC containing RF in both seropositive and seronegative PRs and to a similar degree in a non-negligable percentage of clinically non-classable RICs conforms the diagnostic value of this research. On the other hand there is no relationship between the levels of ICs and either clinical signs or age of the illness. In RPs other than CIR circulating ICs are found whose nature is still unknown.