The distribution of blood to the several tissues of the extremities during rest and exercise has been the topic of much discussion. It is usually assumed that the arteries of the healthy extremity not only can supply the resting needs of the several tissues but can easily carry the extra blood required to perfuse the dilated blood vessels in exercising muscle without depriving the skin or other tissues of the extremity. In arterial occlusive diseases, at least one group of authors has considered the possibility that the arterial blood supply is in fact inadequate to meet the needs of the exercising tissues. According to this concept, the satisfaction of the excess circulatory needs of the exercising muscle is achieved at the expense of the other tissues. If this is the case, the use of exercise in the treatment of peripheral vascular disease may be harmful. The present series of studies