In a randomised, controlled trial of the effectiveness of artificial surfactant therapy 100 babies of less than 34 weeks' gestation were intubated at birth and received manual ventilation. The 49 babies in the treated group also received 30 mg dipalmitoylphosphatidylcholine and 3 mg high-density lipoprotein in a 5 ml suspension. There were no significant differences in mortality or in the incidence or severity of respiratory distress syndrome between the surfactant-treated and control groups as a whole or between subgroups divided on the basis of sex or pulmonary maturity (as assessed by the lecithin-sphingomyelin ratio). However, there appeared to be a trend towards improved survival in treated babies of 27-29 weeks' gestation.