Summary1. Electrical activities of the cerebral cortex and the brain stem, flexion reflex and the muscular tension of the hind limb of rats were recorded and the effect of Myanesin on them studied.2. By administration of Myanesin, muscular tension was first suppressed, the electrical activities of the brain stem and the brain stem factor (peaks in 150 msec) of the flexion reflex were suppressed, and then the cortical activities and the cortical factor (peaks in 200msec. or more) of the flexion reflex curve were suppressed.3. Recovery of the electrical activities and the flexion reflex preceded that of the muscular tension.