Numerous studies have demonstrated the superiority of membrane oxygenators (MO) over the bubble oxygenators (BO) when used for prolonged cardiopulmonary support. However, there is little information available evaluating the MO for routine, short-term cardiopulmonary bypass. In this study the 5MO314 Modulung-Teflo (MO) was compared to 5M30314 Miniprime Variflo (BO). The data of 91 patients (46 MO and 45 BO) were analyzed according to the duration of cardiopulmonary bypass (Group I less than 60 min., Group II 60-90 min. and Group III greater than 90 min.). Hemodynamic parameters, fluid and blood balance, as well as hematologic and blood gas studies were used for comparing the two oxygentors. The hemodynamic parameters were better, and the arterial blood gases were more physilogic with the MO. The postoperative blood loss was significantly less when using the MO. The other measurements documented the stability of the MO. All statements were based on statistical analysis with a DEC PDP-9 computer, using the MIIS language and operating system. Consequently, we are now using this MO for routine cardiopulmonary bypass.