The effect of catecholamine in vivo was studied on purine catabolism in rats and chickens. Catecholamine, administered intraperitoneally in a high dose, markedly increased plasma uric acid and allantoin in rats, and an increase was also observed with intravenous infusion of a lower dose of catecholamine. The effects of catecholamine were characterized by inhibition with alpha and beta adrenoceptor antagonists. Regarding the mechanism of this catecholamine action on purine catabolism, it was shown that catecholamine stimulated degradation of tissue ATP into the end-product. Plasma allantoin, the final purine catabolite in rats, elicited by catecholamine could be maintained under conditions of renal failure, although the action of catecholamine in intact rat was short lasting. The effect of catecholamine was potentiated and/or prolonged by angiotensin-II and aminophylline, and a hyperuricemic state could be induced by catecholamine treatment in chickens. In addition, increase of plasma purine catabolite by immobilization stress in rats suggested the involvement of endogenous catecholamine. From these experimental results, it is considered that catecholamines probably play a important role in the pathogenesis of hyperuricemia.