Arterial hypertension that occurs after severe head injury is characterized by elevation of systolic blood pressure, tachycardia, increased cardiac output, normal or decreased peripheral vascular resistance, and increased circulating catecholamines. The effects of two drugs used in the management of hypertension, propranolol and hydralazine, on these indices of cardiovascular function were examined in six head-injured patients. Both drugs effectively normalized blood pressure. However, hydralazine increased heart rate by 30%, cardiac index by 49%, left cardiac work by 21%, and pulmonary venous admixture by 53%, and was responsible for an increase in intracranial pressure or decreased compliance in two patients. Hydralazine produced no consistent change in arterial catecholamines. In contrast, propranolol decreased heart rate by 21%, cardiac index by 26%, left cardiac work by 35%, pulmonary venous admixture by 15%, and oxygen consumption by 18%. Propranolol decreased arterial epinephrine levels by 48% and norepinephrine levels by 28%. Propranolol appears to be a useful antihypertensive drug in the hyperdynamic head-injured patient because it normalizes blood pressure and the underlying hemodynamic abnormalities both by its beta-adrenergic blocking action and by decreasing circulating levels of catecholamines.