1. In rats with deoxycorticosterone acetate (DOCA) hypertension basal plasma concentrations of noradrenaline and adrenaline correspond to those of sham-treated controls.
2. In DOCA-treated rats frusemide caused a more pronounced increase in plasma noradrenaline than in control rats. This difference was not observed for adrenaline.
3. In the isolated perfused hind-limb preparation the sensitivity to noradrenaline was already enhanced before blood pressure was elevated.
4. These results suggest that the adrenergic vascular tone is increased in DOCA hypertension in rats.