We studied the influence of respiratory distress syndrome (RDS) on the patterns of chest wall movements and respiratory pauses in preterm infants during the first week of life. Eight infants with mild-to-moderate RDS and 10 healthy preterm infants (non-RDS group) were evaluated on Days 1, 3, and 7. Chest wall movements were measured by strain gauges over the upper (URC) and lower (LRC) rib cage and abdomen. Respiratory pauses were determined from both a nasal thermistor and chest wall movements. In the RDS infants the incidence of asynchronous URC and abdominal movements increased from 3 ± 1% and 8 ± 3% (mean ± SEM) on Days 1 and 3, respectively, to 38 ± 5% by day 7 (p<0.01). Furthermore, on Days 1 and 3 asynchronous URC movements occurred more frequently in the non-RDS infants (15 ± 5% and 30 ± 7%, respectively; p<0.05) when compared with the RDS infants, but by Day 7 both groups were comparable. In the RDS infants, respiratory pauses ≥ 5 s and ≥ 10 s were rare on Days 1 and 3 and increased significantly by Day 7, whereas in the non-RDS infants such pauses were as common on Days 1 and 3 as on Day 7. Thus infants with RDS appear to have enhanced respiratory muscle activity resulting in a lower incidence of both asynchronous URC movements and respiratory activity resulting in a lower incidence of both asynchronous URC movements and respiratory pauses during their acute illness. These findings may partially explain the clinical observation that onset of apneic episodes is delayed in some preterm infants. Changes in transcutaneous PO2 and PCO2 and behavioral sleep state did not appear to account for the apparent increase in respiratory drive in infants with RDS, which may be the result of enhanced pulmonary afferent activity.