A male infant with a birth weight of 2,550 g, was born by spontaneous vaginal delivery at 36 weeks' gestation following an uneventful pregnancy. Apgar scores were 5 and 8 at one and five minutes, respectively. Idiopathic respiratory distress syndrome developed in the patient, and he required intubation and mechanical ventilation from 6 hours of age. A chest roentgenogram was done (Fig 1). At 4 days of age, ventilatory requirements increased: with a forced inspiratory oxygen of 0.85 and ventilation at 60 breaths per minute with inspiratory and expiratory pressures of 20 and 3 cm H2O, respectively. A repeated chest roentgenogram was obtained (Fig 2). Selective intubation of the right main bronchus was performed using a size 3.0-noncuffed endotracheal tube. Within two hours of selective intubation of the right main bronchus, the forced inspiratory oxygen requirement had fallen to 0.55, and ventilation pressures were subsequently reduced. Twenty-four hours