Glycopyrrolate, a synthetic quarternary ammonium compound, has a similar pharmacologic property to that of scopolamine, a belladonna alkaloid. Since glycopyrrolate, a quarternary ammonium compound, dose not readily cross the blood brain barrier, it has less central effect than that of scopoiamine a tertiary-amine compound. The authors administered a small dose of scopolamine and glycopyrrolate to human volunteers, and examined the effect on the heart rate ofr both drugs. The results were as follows: 1) A small dose of scopolamine(0.1mg) showed significnat decrease in the heart rate. 2) A small dose of gylcopyrrolate(0.1mg) indeced little change in the heart rate. 3) A small dose of gylcopyrrolate(0.1mg), 10minutes after glycopyrrolate(0.1mg), showed marked increase in the heart rate. 4) A small dose of scopolamine(0.1mg), given 10 minutes after glycopyrrolate (0.1mg), showed tendency for decrease in heart kate. 5) A small dose of gylcopyrrolate(0.1mg), 10 minutes afterscopolamine(0.1mg), showed significant increases in the heart rate. 6) Scopolamine induced bradycardia was suppressed by an additional dose of glycopyrrolate and a preceding dose of glycopyrrolate.