Transcutaneous oxygen tensions (tcPO2) of the lower extremity were investigated in 24 control subjects and in 69 patients with various degrees of peripheral arterial occlusive disease. With a modified Clark-type oxygen electrode, tcPO2 was monitored from the right subclavicular region (position 1), upper calf (position 2), and dorsum of the foot (position 3). The tcPO2 was significantly lower in patients when compared to control subjects. The reproducibility of the method was determined from double determinations of the tcPO2 (position 2) in control subjects. The comparison of tcPO2 value between the right and left lower extremity showed no significant differences. The tcPO2 of the foot or leg showed an increase, when positioning the limb below the phlebostatic level. The response of the tcPO2 after transient arterial occlusion (4 minutes) was significantly delayed in patients compared to control subjects. Finally, preliminary results of 35 patients in whom amputations had been performed suggest that tcPO2 measurement may become a useful prognosticator for the determination of the optimal amputation level.