Thoracic gas volume (TGV) and specific airway conductance (SGaw) were measured in 6 infants, 21–42 weeks of age, who had been mechanically ventilated during the neonatal period. SGaw was significantly decreased while TGV was normal. Administration of a nebulized β2-sympathomimetic stimulant did not improve lung function. It is concluded that inhalation of β2stimulant drugs is not effective in improving airway obstruction in infants with postventilation-elevated airway resistance and that this is likely to be of structural origin.