The current study was undertaken to ascertain whether shift from supine to prone posture alters the pattern of natural breathing in healthy fullterm newborns. Breathing patterns were measured in the supine and prone posture in 20 healthy fullterm infants using calibrated, noninvasive respiratory inductive plethysmography (RIP). The values for breathing pattern components in supine and prone postures expressed as means (+/- SD) were, respectively, tidal volume (VT), 14.1(+/- 3.2) and 18.9(+/- 4.9)mL; mean inspiratory flow 26.7(+/- 11.5) and 32.8(+/- 13.0)mL/s; and minute ventilation 232(+/- 75) and 288(+/- 96)mL/kg/min (P < 0.01). Less thoracoabdominal incoordination, expressed as the labored breathing index (LBI), occurred with shift from supine to prone posture in infants studied in the active behavioral stage, changing from 2.0(+/- 0.5) to 1.3(+/- 0.4) (P < 0.01). Placement of a facemask-pneumotachograph system increased VT measured with RIP by 26% in the supine, and 18% in the prone posture. Neither respiratory rate nor inspiratory time (Ti) changed with the postural shift. Therefore, change from supine to prone posture improved ventilation and increased respiratory drive as expressed by VT/Ti. Further, thoracoabdominal incoordination which took place during active sleep in the supine posture, lessened with change to the prone posture.