The normotensive unanesthetized dog receiving chlorisondamine chloride, pentapyrrolidinium, or hexamethonium exhibits a drop in systolic blood pressure, narrowing of pulse pressure, tachycardia and relaxation of nictitating membranes. The relative potencies of these compounds are in the ratio 8:3:1 respectively. While these compounds are apparently equally well absorbed, the activity of chlorisondamine chloride is markedly prolonged. This prolonged activity of chlorisondamine chloride after oral administration is probably due, in large part, to its persistence in the tissues. Chlorisondamine chloride and hexamethonium can suppress the pressor response induced in neurogenic hypertensive dogs by application of annoying stimuli.