The design of a microcomputer-based monitoring and display system for a cardiopulmonary bypass loop is discussed. Analog signals representing blood temperature and oxygen saturation of sample points entering and leaving the blood oxygenator, patient temperature, oxygenator heat exchanger water temperature and hemoglobin content are monitored and displayed. The hemoglobin content and oxygen saturation signals, input from a reflective-type hemoglobin meter and oximeter are corrected for blood temperature and operator input pH. The oxygen saturation is also corrected for hemoglobin content. Oxygen transfer to the patient is calculated and displayed to evaluate the effectiveness of the system in cardiopulmonary support. Alarms are issued for free gas in blood, no blood flow, and high oxygenator water temperature. The hardware and software design is described along with schematics and flowcharts. A complete software listing is included. The monitoring and display system is operational, but has not been tested with flowing blood. / M.S.