Diagnose and treat hypertensive patients or patients suspected of having neural crest tumors of the adrenal medulla and extraadrenomedullary tissues (pheochromocytoma, neuroblastoma, ganglioneuroma); evaluate patients with orthostatic hypotension. Slight elevations of plasma catecholamines (less than 3-fold) are consistent with essential hypertension, intense physical activity, emotional and physical stress, drug interferences and improper specimen collection. Significantly elevated concentrations (greater than 3-fold), either persistent or paroxysmal, are suggestive of pheochromocytoma.