The effect of close intra-arterial administration of pentobarbital in the concentration of about 2 X 10(-4) mol/l on the venous stasis induced arteriolar constriction in the dog hindleg was studied in 6 neurolept anesthetized dogs. It was found that the blood flows and vascular resistances in the legs before pentobarbital infusion were equal and the vasoconstrictor responses to venous stasis were the same. Pentobarbital infusion into the femoral artery in one of the legs increased the total leg blood flow compared to the control leg and abolished the increase in vascular resistance during venous stasis. In another experimental series the effect of general pentobarbital anesthesia on the vasoconstrictor activity in response to venous stasis locally in subcutaneous and muscle tissue in the hind limb was examined in 6 dogs. It was found that during the first 2-3 h of anesthesia the vasoconstrictor response was present in both tissues although the response in muscle tissue exhibited a great variation between the dogs during this period. However, after 4-5 h of anesthesia the response was abolished in both tissues. During neurolept anesthesia with fentanyl/N2O the same vasoconstrictor response was demonstrated in the hindleg 1 h and 5 h after induction of the anesthesia. It is concluded that pentobarbital anesthesia abolishes the arteriolar constriction induced by venous stasis. The mechanism may be blockade of the local sympathetic vasoconstrictor fibres or interference with myogenic vasoconstrictor mechanism of the vascular smooth muscle cells or both. It is suggested that fentanyl/N2O anesthesia is better suited for this kind of studies.