15 infants weighing 501 to 1000 g, less than 4 h of age, who had received one dose of surfactant and required ventilation with mean airway pressure >4–6 cm H2O and FiO2 >0.25, and had an anticipated duration of ventilation greater than 48 h. Newborns were stratified by birth weight and prenatal steroid status, and then randomized to either HFOV or SIMV with tidal volume monitoring. Ventilator management for patients in both study arms was strictly governed by protocols that included optimizing lung inflation and blood gases, weaning strategies and extubation criteria.