Seven patients (4 with subarachnoid hemorrhage, 2 with intracerebral hemorrhage, and 1 with massive cerebral infarction) had acute arterial hypertension refractory to control by several antihypertensive drugs (hydralazine, sodium nitroprusside, alpha-methyldopa, and trimethaphan camsylate) used singly or in combination. In each case, catecholamine excretion--measured by urinary norepinephrine plus epinephrine--was markedly elevated, averaging 218 microgram/day. Patients without the acute refractory hypertension had normal or only slightly elevated urinary catecholamine levels (mean, 72 microgram/day). The beta-adrenergic blocking agent propranolol, in doses between 20 and 40 mg every 6 hours, successfully controlled blood pressure, while other agents failed. The intense sympathetic nervous system discharge resulting in acute refractory hypertension may be due to injury to the diencephalon or brainstem (or both) or to diffuse brain dysfunction from increased intracranial pressure or intracranial blood.