The response of limb circulation to tourniquet ischaemia in the hind limb of the rabbit was studied. Muscle blood flow was evaluated by means of a local isotope technique using Xe133 as the tracer and the changes occuring after tourniquet ischaemia of 60--180 minutes duration were investigated. The results obtained suggest that even when the tourniquet time is extended to 3 hours, no blood flow occurs in the limb distal to the tourniquet when the cuff is inflated to 300 mmHg. In all animals a hyperaemic reaction was noticed after releasing the tourniquet, and peak reactive hyperaemia was registered 1 minute after the return of circulation. The magnitude of the reactive hyperaemia was independent of the length of tourniquet time. The hyperaemia was regularly of short duration and peak flow values were reached in 1 minute with the flow returning to normal or subnormal values after 5 minuutes. Phlebography studies in 12 rabbits after 120--240 minute tourniquet blockade showed only one thrombosis in a deep popliteal vein after the 240-minute tourniquet time.