Simultaneous measurement was made of isotope clearance and of venous outflow or arterial inflow in the gastrocnemius muscle of anesthetized cats. The purpose was to explore if vasomotor nerves to the skeletal muscles might innervate different types of blood vessels. Restriction of the arterial inflow resulted in approximately proportionate decreases in flow and clearance. Stimulation of the sympathetic supply to the area caused a somewhat greater decrease in total flow than in clearance. Intra-arterial infusion of compound 48/80 or of methacholine, stimulation of the sciatic nerve or of the appropriate anterior roots, all increased flow and clearance proportionately. In contrast, stimulation of vasodilator pathway in the hypothalamus caused significant increase in flow with no consistent change in tissue clearance. With sympathetic stimulation, clearance of intra-arterially injected isotope showed a drop more nearly proportional to the drop in blood flow. None of the vasodilating procedures, however, increased the rate of clearance of intra-arterially administered isotope. It is concluded that most procedures influence the shunt and nutritional blood flow in a proportionate manner, but the active vasodilation resulting from hypothalamic stimulation is restricted to the shunt flow.