1. 1. Blocking the right twelfth thoracic, first and second lumbar nerve roots with alcohol definitely increased the circulation of the right lower extremity in 3 cases of thrombo-angiitis obliterans. 2. 2. This procedure blocks both the sympathetic fibers in the rami communicantes at these levels, as well as the vasomotor fibers in the genitofemoral, femoral, and part of the obturator nerves (somatic). These fibers innervate the aorta, common iliac, external iliac, femoral, and popliteal arteries, and possibly other terminal arteries in the leg and foot. 3. 3. Blocking of somatic muscular and sensory branches of nerves arising from the twelfth thoracic, first and second lumbar roots, produced no serious paresis or paralysis of any muscles, nor any unbearable disturbance in the skin areas supplied by these nerves. 4. 4. The good results obtained from this procedure may be explained as being due to an increase in the circulation of the lower extremity, caused by the removal of an appreciable vasoconstriction status which exists in this disease, either in the diseased vessels themselves, in those not diseased, or in both diseased and non-diseased vessels.