The role of chest wall and vagal afferents on breathing during wakefulness (W), nonrapid eye movement sleep (NREM), and REM sleep was assessed in 16 adult cats implanted with electrodes and skull bolts for sleep recordings with head restraint. Breathing was monitored with a pneumotachograph. Following control recordings establishing characteristic respiratory patterns during each state, cats sustained spinal cord transections at T-1, vagotomies, or both. The transections decreased variability of breathing rate, while vagotomies decreased rate but increased variability and tidal volume. These deafferentations alone or in combination failed to eliminate the major effects of state upon breathing pattern. Different states of consciousness were associated with significant changes on every measured breathing parameter, but the interactions of these effects with the deafferentations were small or nonsignificant. The vagus, however, appears to play its largest role during NREM. We hypothesize that while vagal afference functions during all states to terminate inspiration, during W and REM separate but functionally equivalent mechanisms of central origin supplement the vagus in facilitating the termination of inspiration. The absence of these mechanisms during NREM accounts for the increased vagal influence during this state.