A controlled clinical trial comparing early closure (mean = 48.8 hours) of the patent ductus arteriosus using indomethacin to conventional medical management, with intervention only after cardiopulmonary decompensation (mean = 167.4 hours), was undertaken in 24 preterm infants with severe respiratory distress syndrome and evidence of PDA. An interval analysis of one-half the projected sample revealed that infants undergoing early closure of the PDA had significantly reduced occurrence of BPD or mortality by 6 months of age. A comparison of birth weight, Apgar scores, gestational age, age of initial PDA diagnosis, and fluid therapy during the first seven days of life showed no significant differences between early intervention and control groups. At the time of the interval analysis, there were no differences between the groups in duration of intermittent mandatory ventilation or oxygen exposure. Studies will be required to determine whether these and other variables can be altered by early closure of the PDA.