The aim of this study was to determine the biocompatibility of an auto-oxygenation technique of cardiopulmonary bypass. Forty patients undergoing coronary bypass surgery were studied in two groups: A (auto-oxygenation, patients' lungs used in cardiopulmonary bypass) and B (conventional technique of cardiopulmonary bypass with bubble oxygenator). The platelet count decreased to -73% of initial value in group B vs only -27% in group A, P less than 0.001. Platelet aggregation to ADP decreased slightly in group A and hardly at all in group B, P less than 0.001. A transpulmonary leukocyte sequestration was greater in group B: 1.46 +/- 0.5 x 10(3)/mm3 vs only 0.34 +/- 0.2 x 10(3)/mm3 in group A, P less than 0.001. The level of C3a increased in group A from 244 +/- 46 ng/ml to 418 +/- 34 ng/ml and in group B from 268 +/- 46 ng/ml to 521 +/- 65 ng/ml, P less than 0.001, but in group A the levels were significantly less, P less than 0.001. The current study clearly confirms the superior biocompatibility of cardiopulmonary bypass with lung over oxygenator.