To improve the diagnosis and management of pheochromocytoma, the results from a comparative study of 34 patients with pheochromocytoma, 33 patients with essential hypertension and 36 normal volunteers are presented. Our data suggest that clinical characteristics indicate the possibility of pheochromocytoma only, while the definite diagnosis of pheochromocytoma must be based on comprehensive analysis of all data obtained from both clinical and laboratory studies. The plasma concentration of free norepinephrine in peripheral veins is helpful in establishing the presence or absence of pheochromocytoma. Both CT scan and meta-I-131-iodobenzylguanidine images are useful noninvasive techniques for localization of pheochromocytoma. Phenoxybenzamine is of benefit in both diagnosis and management of patients with pheochromocytoma.