The innervation of skeletal muscle by the lumbar sympathetic nerve was studied through the glyoxic acid histochemical method and the horseradish peroxidase method on 16 anesthesized rabbits. Blood flow changes in the quadriceps muscles during and after stimulation of the sympathetic nerves were evaluated by the heated thermocouple technique in 12 anesthesized rabbits. It seems likely that the postganglionic nerve fibers join to the spinal nerve at the intervertebral foramen and run into the peripheral nerves. The vastus medialis and rectus femoris were mainly innervated by the sympathetic neurons at different segmental levels. Sympathetic disturbance at the segmental level may occur when the spinal nerve is disturbed at the intervertebral foramen. Muscle blood flow decreased after sympathetic nerve stimulation for 1 minute. However, an increase took place after stimulation for 5 minutes. These results suggest the presence of some neurotransmitter present in the postganglionic nerve terminals.