The flow-time curve of resting breathing was recorded in 14 patients (aged 36 +/- 16 yrs) with mild to moderate symptoms of upper airway obstruction (UawO) and compared to that of 28 matched, healthy controls (HC) in order to characterize the breathing pattern of such patients. The inspiratory time over total time (TI/Ttot) was higher in the patients (0.42; SD 0.04) than in HC (0.37; SD 0.04) (p less than 0.001), and tidal volume (VT) over TI was lower in patients (0.37; SD 0.07 l.s-1) than in HC (0.43; SD 0.09 l.s-1) (p less than 0.01). Inspiratory and expiratory peak flows at rest were also lower in the patients (p less than 0.001). In these, the mean to peak flow ratio of inspiration (0.74; SD 0.07) was higher than in HC (0.66; SD 0.04) (p less than 0.0005). This indicates a more rectangular wave of inspiration in the patients. All of these changes may be due to the increased inspiratory load. However, since the patients were breathing at rest with VT and flows far below their values on the maximal flow volume loop, the changes can also be interpreted as adaptive rather than imposed by absolute mechanical limitations.