The manifestation of bioincompatibility in the shape of complement-dependent changes: solubilisation and inhibition--of immune complexed formation was investigated in patients at the prosthetic cardiac operations with using artificial blood circulation, artificial cardiac valves and heterotopic vascular grafts. It was established, that the solubilisation of the precipitate, preformed by plasmic fibrinogen with antifibrinogenic immunoglobulin, and inhibition of hemagglutinating activity of normal autoantibodies in plasma appeared in several minutes after the contact of alien mains with own blood circulation system. These changes of formation of immune complexes in plasma, caused by complement activation, had a selective and reversible nature and were followed breaches of blood circulation. Estimation of early, functional indexes of bioincompatibility, displaying by changes of immune complex formation, may be helpful in prognostic relation in patients with immunocomplex diseases at prosthetic cardiac operations.