Esophagobronchial reflexes have been demonstrated in both the cat and dog models. In order to determine if these reflexes are present in humans and if they are vagally mediated, a prospective sequential study was initiated. One hundred thirty-six individuals referred for esophageal manometric measurements were studied. Measurements of airway flow, arterial oxygen saturation, and pulse rate were performed before and after intraesophageal infusion of sterile water, normal saline solution, and 0.1 N hydrochloric acid. Highly significant reductions in heart rate, airway flow, and arterial oxygen saturation were noted after infusion of normal saline and 0.1 N hydrochloric acid compared with baseline water infusion (P less than 0.001). Graded responses were noted with heart rate: the more acidic the solution infused, the larger the decrement of heart rate. Atropine abolished postsaline/acid decrements of airway flow, arterial oxygen saturation, and heart rate. It is concluded that acid-induced, vagally mediated esophagobronchial reflexes are present in humans.