Ventilatory parameters and respiratory drive with and without an added acute resistive load were assessed in 11 healthy preterm infants and 11 infants with bronchopulmonary dysplasia (BPD). Lung mechanics (breathing frequency, tidal volume, minute ventilation, compliance, and resistance) were determined with esophageal manometry and pneumotachography. Respiratory drive was assessed by determining the airway pressure measured 100 ms after the onset of an inspiratory effort against an occlusion. Infants were studied at baseline and with an external inspiratory resistive load of 213.7 cm H2O/L/s. Infants with BPD had similar breathing frequency, tidal volume, and minute ventilation, lower compliance, and greater resistance and airway pressure at 100 ms than healthy preterm infants at rest. With loading, healthy preterm infants demonstrated increased airway pressure at 100 ms, whereas infants with BPD showed no change. Although the healthy preterm infants had decreased minute ventilation and tidal volume with loading, decreases in ventilation were greater in the infants with BPD. These data demonstrate that infants with BPD have responded to a chronic intrinsic load with increased drive. However, this may result in decreased ventilatory reserve and hence, a limited ability to adapt to acute pulmonary loads. (Pediatr Res 32: 356–359, 1992)