Summary1. Re-establishment of renal blood flow after total renal ischaemia of 4 h duration causes a pressor response in pentobarbitone anaesthetized rats and cats. 2. The pressor response is related to the release of renin from the ischaemic kidney. 3. Spinal section at any cervical level or stellate ganglionectomy abolishes the pressor response but spinal section caudad to the thorax or vagotomy and treatment with hexamethonium have no effect. 4. Spinal section and stellate ganglionectomy interfere with the release of renin and with the pressor response to angiotensin.