In 19 normal adults reserpine administration induced significant changes in the parameters of the second glabellar response (R2): shortening of the latency and duration; decrease of the excitability threshold and complete blockade of the physiological habituation of R2 to the electrical and mechanical stimulation. No changes in the first response (Rl) were observed. All the R2 changes disappeared within about 3 days of drug administration. The Parkinson-like effect of reserpine on the glabellar reflex is discussed in the light of a neurohormonal hypothesis in the control of the polysynaptic pathways biasing R2.