The glucagon hydrochloride test of Lawrence was compared with the standard cold pressor-histamine test in 12 patients with pheochromocytoma and in 35 control patients without tumor. Urinary and blood catecholamine levels and the values for urinary vanilmandelic acid and total metanephrine were also determined. One patient without a tumor had a pressor response after receiving histamine; none had a pressor response after receiving glucagon. Eleven patients with tumor were given 1 mg of glucagon; six had a positive pressor response, and four of these six had a positive response after receiving histamine as well. One patient with tumor responded positively to histamine but not to 0.5 mg of glucagon. Although determination of the level of urinary metanephrine remains the preferred screening test for pheochromocytoma, when adjunctive studies are desired we recommend the cold pressor-glucagon test (1 mg) instead of histamine as the standard provocative pharmacologic test for pheochromocytoma.