Hypertensive crises have been provoked in pheochromocytoma patients by the injection of contrast media during angiography and venography. Fear of similar reactions to intravenous urographic contrast medium injection during computed tomography has led to studies without contrast enhancement when pheochromocytoma is suspected. With extraadrenal pheochromocytomas, intravenous contrast enhancement may be essential for tumor location by computed tomography. The catecholamine responses to injection of urographic contrast medium were examined in eight patients with pheochromocytoma and in 12 undergoing computed tomography for other reasons. Plasma norepinephrine concentrations fell in nonpheochromocytoma patients (p less than 0.005), while in pheochromocytoma patients the response was unpredictable, rising in six individuals, although the mean response was not significant (p greater than 0.35). In five patients the magnitude of the increase in norepinephrine concentrations was large enough to have led to a pressor effect had alpha adrenergic blockade not been used. It was concluded that intravenous urographic contrast medium may elevate plasma catecholamines in a significant proportion of patients with pheochromocytoma, but that with adequate alpha adrenergic blockade this should pose no threat.