Abstract: Captopril is a novel orally active inhibitor of angiotensin Ⅰ coverting enzyme and antihypertensive agent. In the present experiment we have found thati captopril has different effects on blood pressure in various types of stabilized hypertensive rats. Intwo-kidney Goldblatt hypertensive rats gavage of this agent lowered arterial blood pressure markedly. The effect became more marked if hydrochiorothiazide was added. In case of Skelton model addition of hydroclalorothiazide did not lower blood pressure. Captopril failed to reduce blood pressure in one-kidney Goldblatt hypertensive, rats, The mechanism of the various effects as mentioned above is worthof further research.