1. In a group of nine middle-aged patients undergoing varicose vein surgery, cardiac output, right atrial, pulmonary arterial and capillary pressures, and leg blood flow were measured after induction of general anaesthesia but before operation, and also during operation before and after blood substitution.
2. Under anaesthesia, the mean preoperative blood flows in the superficial and common femoral arteries were 160 ml/min and 280 ml/min respectively. These flows are comparable with those obtained in other studies under similar conditions but lower than values obtained in conscious subjects. During the operation the leg blood flow decreased by 24%. As cardiac output remained unchanged, the fractional leg blood flow fell. After transfusion of 900 ml of blood the leg blood flow doubled.
3. It is concluded that anaesthesia, surgical trauma and variations in blood volume greatly influence the leg blood flow and that an adequate substitution of operative blood loss is of utmost importance to achieve an optimum peripheral circulation.