An lectromyographical examination was studied on the normal subject. The actionpotential _??_ the gastrocnemius muscle was recorded combining with the electrical stimulation on the tibial nerve. The record was consisted with two kinds of actionpotentials, the faster was called M-wave and considerd as the actionpotential by the direct stimulation on the efferent fibers, and the later was called H-wave (Hcffman's wave) and considerd as monosinaptic reflex actionpotential. 1. The H-wave and M-wave appeard to have rather unstable amplitude even by the same parameter of stimulation in the lower voltage, but showed more stable amplitude in the higher voltage on the same subject. At maximum stimulation for H-reflex, the fluctuation index of H-reflex amplitude was 5.4% , and the same of M-reflex amplitude was 7.9% . 2. No influense on the amplitude of H-reflex was observed by selective procaine bolck of γ fiber in the tibial nerve. 3. The fluctuation of H-reflex amplitude was increased by a voluntary contraction of the gastrocnemius muscle. 4. No relationship was observed between the fluctuation of H-reflex amplitude and respiratory movement.