From February 1975 until July 1976 12 patients who elective surgery and 15 trauma victims received intraoperative autotransfusion. The effects of this method on these patients were controlled by monitoring the behaviour of circulation and of important laboratory parameters. The procedure was well tolerated: 1. Only three of 29 patients showed evidence of cardiac insufficiency (lowering of ST. elevated T-peak, low blood pressure, high central venous pressure) which disappeared after reducing the rate of infusion. --2. Blood pressure, pulse rate and central venous pressure were stable at the end of the operation. --3. There was no renal insufficiency under dopamine (210 microgram/min) and 15% manitol (250 ml i.v.). --4. Serum creatine showed only minor changes from the initial level during the time of observation. --5. The same was true for beta2-microglobulin. --6. Serum urea rose slightly during 7 days. --7. There were minor changes of electrolytes without hypocalcaemia or high potassium. --8. The observed changes showed no relation to the method of anticoagulation and to time or volume of autotransfusion.