To determine whether multiple doses of bovine surfactant would improve neonatal mortality in very premature neonates, we conducted two multicenter controlled trials under identical protocols; the results were combined for analysis. Four hundred and thirty neonates born between 23 and 29 weeks gestation and weighing 600 to 1250 g at birth were assigned randomly at birth to receive either 100 mg of phospholipids/kg of Survanta, a modified bovine surfactant (n = 210), or a sham air placebo (n = 220) within 15 minutes of birth. Neonates who developed respiratory distress syndrome and required mechanical ventilation with at least 30% oxygen could be given up to three more doses in the first 48 hours after birth. Dosing was performed by investigators not involved in the clinical care of the neonates; nursery staff were kept blinded as to the treatment assignment. Cause of death was determined by a panel of three independent, board-certified neonatologists after blindly reviewing case report forms and autopsy reports. Fewer Survanta-treated neonates died of any cause (11.4% vs 18.8%, P = .031), died of respiratory distress syndrome (1.9% vs 15.6%, P less than .001), and either died or developed bronchopulmonary dysplasia due to respiratory distress syndrome (39.5% vs 49.1%, P = .044). The incidence of respiratory distress syndrome was also lower in Survanta-treated neonates (28.0% vs 56.9%, P less than .001), and the Survanta-treated neonates' oxygenation and ventilatory status were improved significantly at 72 hours. Survanta-treated neonates were also at lowered risk of developing pulmonary interstitial emphysema (23.3% vs 36.9%, P = .002) and other forms of pulmonary air leaks (9.6% vs 20.8%, P .002).(ABSTRACT TRUNCATED AT 250 WORDS)