Since Goldenberg, Snyder and Aranow1 reported their experiences using 2-(1-piperidylmethyl)-1,4-benzodioxan (933 F) in the diagnosis of hypertension caused by circulating epinephrine liberated from functioning tumors of the adrenal medulla, many have confirmed their results. Possibility of failure and value of other tests have been reviewed by Roth and Kvale.2 It is well known that pheochromocytomas, whether associated with paroxysmal or persistent hypertension, are removed with difficulty because anesthetic agents and operative manipulation often cause excessive elevations or fluctuations of blood pressure and subsequent reduction and shock. The present high surgical mortality rate (3 of 20 operations reported in the literature since 1943, as reviewed by Hatch, Richards and Spiegl3) is attributed to epinephrine intoxication. Injection of epinephrine can cause increase or decrease of blood pressure. Also, tumors may contain epinephrine or non-epinephrine.4 Behavior of a patient who has a pheochromocytoma with circulating epinephrine and who is