We examined the movements of the vocal cords during tidal breathing, panting, and large changes in lung volume in 12 normal subjects. The glottis was observed with a fiber-optic bronchoscope, and the glottic image was recorded together with flow, volume, and a time marker onto videotape. Phasic respiratory swings in glottic width (dg) and glottic area (Ag) were reproducible in all subjects but differed substantially between subjects. In the group as a whole dg and Ag increased during inspiration to 10.1 +/- 5.6 mm and 126 +/- 8 mm2 (mean +/- SE), respectively, whereas during expiration the lowest values were 5.7 +/- 0.5 mm and 70 +/- 7 mm2, respectively. These extreme dimensions corresponded closely to the midtidal volume points in the respiratory cycle. Glottic width during vital capacity (VC) expirations was nearly 30% greater at a flow of 1.2 l/s than at 0.5 l/s, but the relationship between dg and lung volume differed between subjects. When swings in dg were minimized by panting, there was no difference in dg between functional residual capacity (FRC) and a volume corresponding to midinspiratory capacity. However, tidal breathing at this lung volume was associated with a 20% decrease in dg compared with breathing at FRC. Our observations indicate a tight coupling between the pattern of glottic movement and the respiratory volume cycle. The results suggest that during voluntary respiratory maneuvers both intrinsic laryngeal and respiratory muscles are recruited, participating as effector organs in ventilatory and respiratory control.