Oxygen and carbon dioxide tensions were measured pre- and postoperatively in the gastrocnemius muscles of 6 patients undergoing an aorto- femoral reconstruction due to occlusive arterial disease. Four volunteer patients showing no signs of arterial ischaemia formed the control group. Continuous recordings of tissue gas tensions were carried out by means of an implanted Silastic tonometer during rest and heel lifting exercise. The preoperative measurements were performed a few days to a few weeks prior to surgery and the postoperative determinations 3-6 months after operation. In preoperative measurements of patients with limb ischaemia calf muscle PO2 levels during rest were only slightly lower than in controls, while no differences were detected in the corresponding PCO2 values between the two groups. Arterial surgery elevated the levels of basal tissue PO2 measured at rest. During and immediately after a preoperative exercise test of patients with arterial occlusive disease the muscle PO2 decreased sharply and the PCO2 increased. When the heel lifting exercise test was repeated postoperatively in these patients the calf muscle PO2 and PCO2 underwent no essential changes from the pre-exercise levels. In control patients calf muscle gas tensions showed a totally different behaviour during and immediately after exercise: both PO2 and PCO2 increased moderately. During rest following the exercise test tissue gas tensions resumed their original levels within a few minutes in both patient groups. When the heel lifting exercise was repeated after 20-30 minutes, analogous changes of tissue gas tensions were observed. To summarize, the present data show that pre- and postoperative recordings of calf muscle PO2 and PCO2 combined with an exercise test provide an accurate means of evaluating the change of tissue perfusion and nurtrition after an arterial reconstruction.