The origin of increased plasma uric acid in l-epinephrine-induced hyperuricemia was studied. It was shown that uric acid is increased by an extra-hepatic process, in particular by reduction in the intestinal adenosine-tri-phosphate level. Further, from evidence for the existence of plasma xanthine oxidase, it was shown that production of uric acid by an extra-hepatic process is very likely in many mammals, even in man.