A 46 year old woman suffered five episodes characterized by hypotension, pulmonary edema, ventricular arrhythmias and cardiopulmonary arrest. She was found to have increased urinary total metanephrine and vanillylmandelic acid excretion and a mass in the left adrenal gland was detected on computed tomographic scanning. Because of the clinical picture of an epinephrine-secreting pheochromocytoma, she was prepared for adrenalectomy only with a beta-adrenergic blocking agent. Hypertension did not develop preoperatively. Surgery was complicated by severe hypertension, with blood pressure levels as high as 240/130 mm Hg, requiring the intravenous administration of alpha-adrenergic blocking agents. Plasma epinephrine and norepinephrine values, determined preoperatively but reported postoperatively, confirmed the presence of markedly elevated plasma epinephrine levels (1,210 and 1,840 pg/ml). Notably, however, plasma norepinephrine concentrations were also increased (1,980 and 3,000 pg/ml) and the tumor contained large amounts of norepinephrine as well as epinephrine. Thus, combined norepinephrine secretion was documented in a patient with the clinical picture of an epinephrine-secreting pheochromocytoma. In our judgement, such patients should be prepared for surgery with both beta- and alpha-adrenergic blocking agents. This patient exemplified the utility of isotope derivative measurements of plasma norepinephrine and epinephrine concentrations in the diagnosis of pheochromocytoma. Of 15 patients with surgically proved pheochromocytomas studied in our laboratory, plasma catecholamine concentrations were increased in all 14 with clinical manifestations compatible with catecholamine excess. Plasma catecholamine concentrations were not distinguishable from normal in one patient studied only because of a family history of pheochromocytoma.