The effect of chronic angiotensin AT1 receptor blockade by a specific antibody on the development of two-kidney, one-clip renal hypertension was studied in Wistar rats. Renal artery constriction resulted in a fast and large increase in blood pressure in comparison with that of control rats. On the other hand, the pre-immunization of rats with a small part of the angiotensin AT1 receptor completely prevented the development of renal hypertension. We conclude that the development of two-kidney, one-clip renal hypertension can be blocked by a specific antibody raised against a part of the angiotensin AT1 receptor.