The effect of an euglycemic-hyperinsulinemic glucose clamp (94 +/- 5 microU/ml) on blood flow and glucose extraction fraction in human skeletal muscle and adipose tissue was investigated. Limb blood flow was measured by venous occlusion pletysmography and tissue blood flow by the microdialysis ethanol technique. Insulin infusion resulted in an increased blood flow in the calf and forearm (64 and 36%, respectively; P < 0.01) but not in the studied muscles of these limbs (ethanol outflow-to-inflow ratio: m. gastrocnemius 0.144 +/- 0.009 to 0.140 +/- 0.011, NS; m. brachioradialis 0.159 +/- 0.025 to 0.168 +/- 0.027, NS). This was accompanied by an increased extraction fraction of glucose, as measured by an increased arteriovenous difference over the forearm (0.16 +/- 0.04 to 0.70 +/- 0.10 mmol/l; P < 0.001) and by an increase in the estimated arterial-interstitial glucose difference in the gastrocnemius (0.82-1.42 mmol/l) and brachioradialis muscle (0.82-1.97 mmol/l). The blood flow in adipose tissue was significantly increased during insulin infusion, as evidenced by a decreased ethanol outflow-to-inflow ratio (0.369 +/- 0.048 to 0.325 +/- 0.046; P < 0.01). This was accompanied by an unchanged concentration of glucose in the dialysate (-2.6%, NS). In summary, during physiological hyperinsulinemia 1) a blood flow increase was detected in the calf and forearm, but not in the studied muscles of these limbs; 2) the blood flow increased in the subcutaneous adipose tissue; and 3) the estimated arterial-interstitial glucose difference increased in both muscles studied and was larger in the forearm muscle than the arteriovenous glucose difference over the forearm. The present study shows that microdialysis is a useful tool to obtain tissue-specific information about the effect of insulin on blood flow and glucose extraction in human skeletal muscle and adipose tissue.