Platelet norepinephrine and epinephrine concentration in patients with pheochromocytoma. Platelet and plasma catecholamine concentrations were determined in 17 patients with surgically proven pheochromocytoma (mean age 42.3 years); in 31 patients with borderline hypertension (mean age 35.3 years) and in 9 healthy controls (mean age 39.3 years). Both platelet norepinephrine and epinephrine were significantly increased in patients with pheochromocytoma when compared with hypertensive and control groups (P less than .001). No correlation between platelet and plasma catecholamines was detected in all studied groups. The diagnostic accuracy of platelet catecholamine in pheochromocytoma is limited since increased platelet norepinephrine was found in 35.5% and increased platelet epinephrine was found in 19.4% of patients with essential hypertension. 