Recent reports suggest that endogenously released endorphins may exert a modifying influence on respiratory center drive in patients with respiratory disease. In this report, we employed respiratory inductive plethysmography to noninvasively assess breathing patterns with particular attention to respiratory center drive as reflected by mean inspiratory flow. We studied 10 patients with documented chronic obstructive pulmonary disease (6 with hypercapnia and 4 with normocapnia) after treatment with placebo and the opiate antagonist, naloxone. No significant change in breathing pattern was observed in either patient group after treatment with placebo or naloxone, although individual patients displayed greater respiratory drive after naloxone than placebo. Therefore, endorphins do not exert a consistent influence on respiratory center output in patients with chronic obstructive pulmonary disease.