Introduction Reports on the clinical results of lumbar sympathectomy have varied from great satisfaction to the denial of any essential benefit.1,2 Clinical evaluation of therapeutic results in chronic disease is notoriously difficult.3 On the other hand, it must be admitted that a rationale established on purely experimental basis may not necessarily always be borne out by clinical experience. Nevertheless, if reliable methods to ascertain the physiologic effects of a procedure are available, it is preferable to establish such on an objective basis rather than to rely on clinical impressions. With this in mind the effects of lumbar sympathectomy upon blood flow to skin and muscles of the lower extremity in patients with arteriosclerosis obliterans were measured plethysmographically. Methods and Material Presympathectomy measurements of blood flow were made on 12 limbs in eight patients with non-gangrenous obliterative atherosclerosis. In six, unilateral sympathectomy was performed and post-sympathectomy data (two to