Clonidine (Catapres) administered intramuscularly in a dose of 150 microng produced a satisfactory reduction in blood pressure in 13 of 16 hypertensive patients. Its effect occurred within five minutes, was maximal at 75 minutes and persisted for five hours. In six patients who received two doses (150 microng and 300 microng), the response was shown to be dose-related. No serious side effects were noted. Intramuscular administration of clonidine thus appears to be safe and effective. It has a place in the management of uncontrolled hypertension when a rapid reduction in blood pressure is undesirable and in the maintenance of blood pressure control when oral therapy cannot be tolerated.