Sixty-five coronary patients were subjected to aortocoronary bypass surgery. Three groups were distinguished: 1) controls-no filters; 2) patients in whom hemotransfusion (40 mu) and infusion filters were used during and on day 1 after surgery; and 3) in whom leukocyte filters for filtering residual perfusate from artificial circulation device were used in addition to the filters used in group 2. In the controls plasma level of leukocytic alpha-glycoprotein after artificial circulation increased 22 to 36 times, whereas in groups 2 and 3 it did not increase at all. After surgery the severity of leukocytosis, hyperthermia, and hyperenzymia assessed from the level of SGOT was reliably lower in patients in whom the filters were used. The time course of the oxygenation index (PaO2/FiO2) indicated an improvement of gas exchange due to filtration of infusion-transfusion media. The minimal values of PaO2/FiO2) and plasma content of C-reactive protein were observed in group 3. The mechanisms of systemic inflammatory reaction and organ dysfunction and some aspects of the protective effect of filters are discussed.