Since narcotic drugs profoundly depress breathing, we tested whether endogenous opioids influenced control of breathing in chronic obstructive pulmonary disease (COPD), reasoning that the stress of chronic dyspnea might cause elaboration of "endorphins." In 14 patients with COPD (but without respiratory failure) and eight normal controls, we measured ventilation, mechanical lung function, respiratory sensitivity to carbon dioxide, and the increase in respiratory effort elicited by an increase in resistance to breathing; each measurement was performed before and after administration of the opiate antagonist naloxone. Before naloxone, increased resistance to breathing enhanced respiratory effort in all controls, but seven of 14 patients with COPD had no response. After naloxone, these seven patients had load responses. Furthermore, the respiratory effort elicited by the resistance also increased after the drug was given to the patients who had had a response. These data suggest that endorphin elaboration minimizes the stress of chronic airway obstruction.