Cardiopulmonary bypass surgery may be complicated by a systemic inflammatory reaction, which has been ascribed to activation of complement. For such activation, the choice of priming solution for the heart-lung machine may be of importance. The peripheral blood of three groups of eight donors was exposed to albumin, hydroxyethyl starch (HES) or to HWA-138 (pentoxifylline analogue) in addition to the priming solutions. The study confirmed that activation of complement is a consistent phenomenon during cardiopulmonary bypass surgery. The concentration of the C3 activation product C3a in the plasma was significantly increased after simulated extracorporeal circulation. However there were no differences within the increase of C3a concentrations between the various priming solutions.