Currently the only treatment available for inoperable pheochromocytoma is symptomatic and palliative with alpha- and beta- adrenergic blockade. Pheochromocytoma is a tumor of chromaffin tissue derived from the neural crest and closely related to other APUD (amine precursor uptake and decarboxylation) cell tumors, including those of the pancreatic islets. Streptozocin has been used with varying success in some of these tumors and therefore merited a trial in pheochromocytoma. We used streptozocin to treat two patients with inoperable pheochromocytoma; the drug failed to have any effect, either on catecholamine excretion or tumor growth.