To assess the efficacy of a multiple-dose protocol of surfactant replacement therapy in neonates of 30 to 36 weeks' gestation, 75 neonates were randomly assigned to control, single-dose surfactant, or multiple-dose surfactant groups. Neonates at less than 6 hours of age with a diagnosis of respiratory distress syndrome were eligible. Subjects were randomly assigned to receive either 100 mg/kg of bovine surfactant or air placebo. Neonates in the multiple-dose group were eligible to receive up to three additional doses as indicated. Neonates in both surfactant groups showed a positive response to treatment, with marked improvement in oxygenation by 10 minutes postinstillation (P less than .0001). Both surfactant groups had better oxygenation than control subjects at lower ventilatory parameters over the first 24 hours. A deterioration in oxygenation and ventilatory requirements was seen in both treatment groups starting 6 to 12 hours after the first dose. The deterioration in oxygenation could be minimized by the use of multiple doses; however, extra doses had no effect on diminishing ventilatory requirements or time to extubation. It is concluded that surfactant therapy at less than 6 hours of age is effective in acutely reducing oxygen and ventilatory requirements in neonates of 30 to 36 weeks' gestation with respiratory distress syndrome. It appears that multiple doses of surfactant have a greater effect on sustaining improvements in oxygenation than on ventilatory requirements. Further study is required to determine optimal dosage and retreatment strategy.