The effects of the sympathetic nerve on the muscle blood flow were studied on the quadriceps muscles of anesthetized rabbits. The muscle blood flow was measured by heated thermocouple technique, electrolytic hydrogen clearance method and laser doppler flowmetry. There was significant correlation in the muscle blood flow measured by the above three methods. After blockage of the neuro-muscular junction with pancuronium bromide, the femoral nerve stimulations with pulse duration 0.1 msec, 6 V, at 2, 5 and 10 Hz caused no change in the muscle blood flow, while the stimulation with pulse duration 1 msec, 6 V, at 10 Hz caused reduction of the muscle blood flow. The higher the frequency of lumbar sympathetic trunk stimulation was, the lower the muscle blood flow became thus the longer the recovery time was. When femoral nerve and lumbar sympathetic trunk were stimulated simultaneously, increment of muscle blood flow during contraction became less prominent, especially, with a stimulation of 5 Hz, which caused a decrement of post-contraction hyperemia both in height and duration. These results suggest that sympathetic nerve activities have an influence on the muscle blood flow at rest, as well as during and after muscle contraction.