The strategy of non-selective neuromuscular paralysis was compared with that of synchronised (fast rate) ventilation and selective paralysis in infants receiving mechanical ventilation for respiratory distress syndrome with chronic lung disease as the primary outcome measure. One hundred and ninety three infants weighing under 2000 g were randomly allocated to receive either pancuronium during mechanical ventilation in the acute phase of respiratory distress syndrome (non-selective group) or synchronised ventilation (initial ventilatory rate at or above that of the infant's) (selective group). Infants in the selective group received pancuronium if they were consistently expiring during the inspiratory phase of the ventilator cycle. There was no significant difference between the groups with respect to birth weight, gestation, and sex distribution. There was no significant difference between the group with respect to death (selective 19%, non-selective 16%), pneumothorax (selective 14%, non-selective 14%), chronic lung disease (selective 49%), non-selective 47%), and oxygen dependency at 36 weeks' postmenstrual age (selective 32%, non-selective 39%). Routine paralysis of ventilated infants has potential complications that may be avoided by using synchronised ventilation. As the latter is not associated with an increased incidence of long term respiratory complications, it is concluded that it is the optimum strategy of the two for ventilating infants with respiratory distress syndrome.