Hypertension was induced in rats by renal artery clip with the contralateral kidney removed (Goldblatt I) or left intact (Goldblatt II). 2. Plasma noradrenaline was increased 62% in the Goldblatt I animals after 3 weeks. 3. Hypothalamic tyrosine hydroxylase and dopamine beta-hydroxylase activities, and the concentration of noradrenaline were increased in the Goldblatt I animals after 3 weeks. 4. Enhanced hypothalamic noradrenaline synthesis may be a pathogenic factor in Goldblatt I renovascular hypertension.