Labetalol is a new adrenergic antagonist with both alpha- and beta-blocking effects. To evaluate its usefulness in the treatment of hypertension in patients with coexisting chronic obstructive pulmonary disease (COPD), labetalol was administered in gradually increasing doses to a group of 11 patients with mild-to-moderate hypertension and COPD with a mild reversible component. Ten patients given hydrochlorothiazide served as control subjects. Blood pressure was controlled in seven of the 11 patients given labetalol and in six of the ten patients given hydrochlorothiazide in dosages up to 1,200 mg/day and 150 mg/day, respectively. No significant changes occurred in the FEV1 or FEF25-75% two hours after the administration of the maximum dose of either drug or after exercise on the same day. Labetalol was well tolerated in the doses given.