In in-vitro study, human immunoglobulin (Ig) denatured by O2 bubbling markedly produced C4a, C3a, and C5a, whereas human albumin treated identically did not. White blood cells (WBC) treated by O2 bubbling significantly increased C3a levels alone, but at a much lesser grade than the Ig. A new priming method, i.e., homologous concentrated red cell (CRC) and human albumin was discerned from the experimental facts in-vitro, and we investigated the clinical effects of that priming method. C4a, C3a and C5a in BOG primed with homologous whole blood (HWB) were slightly higher than those in MOG during CPB. Those in the Ig-free priming group were more mildly increased than those in the HWB priming group, not only during CPB, but also after protamine administration; this tendency was clearer in BOG. It is concluded that (1) human immunoglobulin (Ig) denatured by O2 bubbling produces anaphylatoxins via the classical pathway; (2) WBC treated identically produces C3a at a far milder grade; (3) priming with CRC and human albumin reduces plasma anaphylatoxin levels; and (4) pulmonary function at an early postoperative period was improved in the homologous Ig-free priming group, especially with BOG.