Pressor responsiveness to angiotensin II and noradrenaline have been examined using a blood perfused hind limb preparation in early and chronic renovascular hypertension before and after correction of the hypertension by removing the renal artery clip. Hypersensitivity was only partially developed in the early phase but markedly so in the chronic phase. After renal artery unclipping blood pressure returned to normal within 24 h despite the continued presence of enhanced vascular reactivity. When studied 60 days after unclipping, pressor responsiveness had returned to normal in both previously early and chronic hypertensive rats. These results suggest that hypersensitivity to pressor agents develops after hypertension has become established and as a consequence of structural vascular change in response to the raised blood pressure. Although these changes may play a role in the maintenance of blood pressure in chronic hypertension they are of little importance in the development of hypertension.