The exposure of blood to foreign materials can cause the denaturation of plasma protein components such as immunoglobulins and complements. And those phenomena increase the morbidity and mortality after intracardiac operations through the cardiopulmonary bypass. From April, 1987 to September, 1987, we had observed the serial changes of plasma total protein IgG, IgA, IgM, complements[C3, C4] in bubble oxygenator group[n=5] and membrane oxygenator group[n=5]. Statistically significant difference between two groups were present in total protein and C3. We conclude that using membrane oxygenator in long extracorporeal circulation can reduce the activation of alternative pathway of complement system, and which can reduce post-perfusion complications of the lung though we can`t prove it in mass populations.