The effects of constant positive airway pressure applied via a nose mask through the nares (nasal CPAP) on the swallowing reflex were studied in eight adult humans. The swallowing reflex was induced by bolus injections of a small amount of distilled water (0.5 ml) into the pharynx at four different values of endexpiratory airway pressure (0,5,10, and 15 cm H2O CPAP) or by continuous infusion of water (3 ml/min) at two different values of endexpiratory airway pressure (0 and 15 cm H2O CPAP). The latency of response from the time of bolus injection of water to the occurrence of the first swallow as well as the number of swallows elicited during the period of 10 s immediately following the water injection were measured. Our results showed that increases in endexpiratory airway pressure progressively prolonged the latency of response and decreased the number of swallows. Also, the frequency of swallows decreased greatly at nasal CPAP of 15 cm H2O during continuous infusion of water. These results indicate that nasal CPAP exerts an inhibitory influence on the swallowing reflex.