SummaryClonidine or ST 155 or Catapressan (R) is a rather active antihypertensive drug, indicated in the acute and chronic treatment of moderate and severe essential and secondary hypertension.The mechanism of antihypertensive action is probably related to the inhibition of the cardiovascular centers of the central nervous system, resulting at least in acute experiments in bradycardia, a decreae of the cardiac output and flow in several organs, without important changes in the peripheral resistance.In men no important metabolic disorders or tissue damage have been described up to now, but side-effects as sedation, dryness of the mouth, pallor, and constipation are frequent.Orthostatic hypotension is rare.Detailed schemes for acute and chronic treatment of essential and secundary hypertension with Clonidine in association with diuretics are described.