Wide pulse pressure is considered to be a sign of patent ductus arteriosus (PDA). We tested the hypothesis that, following indomethacin therapy, PDA closure is associated with a significant decrease in pulse pressure. Thirty-two ventilated preterm infants were echocardiographically diagnosed within the first 24 hours of life with PDA. Systolic, diastolic, and mean arterial blood pressures were measured prior to indomethacin treatment and after echocardiographically confirmed PDA closure. Following PDA closure, systolic and diastolic blood pressures and mean arterial pressure increased significantly without a significant change of pulse pressure (17 ± 7 to 20 ± 12 torr). We conclude that in preterm infants with PDA, systolic, diastolic, and mean arterial blood pressures increase significantly within first few days of life. Pulse pressure does not appear to be affected by early PDA closure. We speculate that high pulmonary resistance in the first days of life prevents significant diastolic aortic runoff and leaves pulse pressure unaffected by PDA, as well as by its closure.