Adrenal catecholamine contents were measured spectrofluorometrically by CROUT'S method in 29 male spontaneously hypertensive rats at the prehypertensive, early and advanced hypertensive stages and in 24 age-matched male normotensive Wistar rats. Adrenal noradrenaline contents per adrenal, per animal, and per gram of adrenal weight in spontaneously hypertensive rats were almost twice as high as those in the controls throughout these stages. Adrenaline contents per adrenal were larger in the early hypertensive stage in the former rats, especially in the advanced one, but no great differences in adrenaline content per gram of adrenal weight were noted between the former and latter groups.