The resting breathing pattern in 14 chronic C6 and C7 traumatic quadriplegics was compared with six age-matched healthy controls. All quadriplegics had complete motor loss below the lesion level and were at least two years postinjury. Tests were performed with subjects seated. Forced vital capacity (FVC), forced expiratory volume in one second (FEV1.0), inspiratory capacity (IC), and maximum inspiratory mouth pressure (Pimax) were measured. Resting breathing pattern was assessed for 20 minutes using mercury in rubber strain gauges and a computer-assisted data acquisition and analysis program. Inspiratory time (Ti), expiratory time (Te), and tidal volume (Vt) were measured, and the remaining timing components were calculated from these values. The variability of breathing was assessed by comparing the coefficients of variation of each variable. The FVC, IC, and Pimax were significantly reduced; Vt was significantly lower (p less than 0.01) and frequency significantly elevated (p less than 0.05) in quadriplegics. The decreased Vt in quadriplegics was due entirely to a significantly decreased mean inspiratory flow (p less than 0.01); Ti was the same in quadriplegics as in controls. The ratio of mean Ti to total cycle time (Ti/Ttot) was significantly longer in quadriplegics (p less than 0.005). There was no difference in variability of breathing between the two groups for any timing component of ventilation. There was no significant difference in sighing frequency between groups for either breaths greater than 2x mean Vt or breaths greater than 3x mean Vt. Chronic quadriplegics demonstrated a rapid, shallow breathing pattern, probably due to the mechanical restrictions resulting from paralysis of the thorax musculature. They retained the ability to sigh, suggesting that chest wall afferents may not be required in this process.