Three patients with history of documented hypotension, near syncope, or syncope before or after the administration of isoproterenol during head-up tilt table are reported. Severe bradycardia was also noted in one patient. All three patients responded to the administration of 2.5 mg of oral dextroamphetamine 45 minutes prior to a repeat head-up tilt table study. The potent central and peripheral adrenergic agonist pharmacological properties of this drug permitted the prevention of severe vasodepressor syncope in these patients.