1. Noradrenaline content of several rat brain stem and hypothalamic nuclei falls transiently at 72 h after initiation of renovascular hypertension (one-kidney Goldblatt model).
2. Tyrosine hydroxylase activity is significantly reduced in posterior, paraventricular and periventricular nuclei of hypothalamus at this time but returns to control value by 7 days.
3. Treatment with hydrallazine, 5 mg/kg intraperitoneally, twice daily or methoxamine, 5 mg/kg, three times daily for 3 days respectively raises and lowers the noradrenaline content of brain nuclei, suggesting that short-term changes in noradrenaline may be secondary to afferent baroreceptor input.
4. At later times after the development of renovascular hypertension (7 and 28 days) activity of phenylethanolamine-N-methyl transferase is increased in the nucleus of the solitary tract and the locus coeruleus.
5. Brain catecholamines may participate both early in the development and later in the maintenance of renovascular hypertension.