Our aim was to investigate the effects of the negative pressure reflex on mechanically opposing pharyngeal muscles during wakefulness, slow-wave sleep (SWS), and rapid eye movement (REM) sleep. In four goats with isolated upper airways, we measured tracheal airflow and electrical activity of the thyropharyngeus (TP; constricting), the stylopharyngeus (SP; dilating), and the diaphragm (Dia). In the wakefulness state in response to negative pressure tests, TP decreased (65%), SP increased (198%), and tidal volume (V-T) (66%) and rate of rise of Dia (Dia(slope), 69%) decreased (P< 0.02). Similarly, during SWS, the negative pressure response of TP (31%), V-T (61%), and Dia(slope) (60%) decreased, whereas SP (113%) increased, relative to SWS control (P< 0.02). In REM sleep, the negative pressure response by TP and SP were small, whereas both V-T (38%) and Dia(slope) (24%) were greatly decreased (P< 0.02) compared with REM control. Inspiratory duration remained unchanged in response to negative pressure tests in all states. These data provide evidence that mechanically opposing inspiratory and expiratory pharyngeal muscles are reciprocally controlled and their response to negative pressure are state dependent.