Augmentation of cutaneous blood flow by postganglionic lumbar sympathectomy may not reflect an increase in nutritive vascular supply to the dermal tissues. Transcutaneous oxygen tension (TcPO2) was compared with radionuclide microsphere determination of dermal microcirculation in a hind limb sympathectomy model in 20 dogs. After 90 minutes the TcPO2 was greater in the sympathectomized limbs than in the contralateral limbs (125 mm Hg versus 114 mm Hg, p < or = 0.05). In contrast, microsphere-determined paw dermal capillary flow declined in sympathectomized limbs (4.9 ml/min/100 gm versus 11.8 ml/min/100 gm, p < or = 0.05). Decreases in the TcPO2/venous PO2 ratio correlated with sympathectomy-induced increases in total limb blood flow (r = 0.60; p < or = 0.001), reflecting less efficient oxygen extraction. These observations confirm the lack of enhancement of tissue oxygen delivery by sympathectomy because of the associated dilation of cutaneous arteriovenous shunts.