Unilateral surgical renal denervation was performed in dogs. 1–2 weeks later, bilateral renal arterial blood flow and central arterial blood pressure were measured. The effect of single intravenous doses of noradrenaline was studied, with or without pretreatment with the α-receptor-blocking agent phentolamine. Complete sympathetic denervation was controlled by fluorescence histochemistry. Vascular resistance increased more in the denervated than in the non-denervated kidney, probably because of the denervation supersensitivity which had developed. Phentolamine pretreatment almost abolished the changes in flow and resistance. The results seem to be of special relevance for transplantation surgery.