STUDY OBJECTIVES: Obstructive sleep apnea (OSA) is characterized by repetitive pharyngeal collapse during sleep. Several techniques have been proposed to assess the collapsibility of the upper airway in awake humans, but sleep-wake comparisons have rarely been attempted and there are few studies comparing OSA patients to control subjects. We sought to compare two collapsibility measurement techniques between normal and apneic subjects, and between wakefulness and sleep. DESIGN: We conducted three studies. First, we examined whether collapsibility assessed by negative pressure pulses (NPPs) during wakefulness reflected values during sleep in 21 normal subjects. Second, we determined in these normal subjects whether collapsibility during sleep assessed by NPPs was predictive of collapsibility measured by inspiratory resistive loading (IRL). Finally, we compared upper-airway collapsibility between apnea patients (n = 22) and normal volunteers (n = 38) during wakefulness by NPPs. SETTING: Clinical and research laboratories at the Brigham and Women's Hospital. PARTICIPANTS: Two populations of normal subjects (n = 21 and n = 38) and OSA patients (n = 22). MEASUREMENTS AND RESULTS: Collapsibility during wakefulness, as measured by NPPs, correlated significantly with collapsibility during sleep (r = 0.62; p = 0.003). There was also a significant correlation between the two measures of collapsibility (IRL and NPP) during sleep (r = 0.53; p = 0.04). Both measures revealed a significant increase in pharyngeal collapsibility during sleep as compared to wakefulness. Finally, apnea patients had significantly greater pharyngeal collapsibility than control subjects during wakefulness (p = 0.017). CONCLUSIONS: These data suggest that upper-airway collapsibility measured during wakefulness does provide useful physiologic information about pharyngeal mechanics during sleep and demonstrates clear differences between individuals with and without sleep apnea.