This clinical trial will attempt to demonstrate if pre-term infants may benefit from treatment with nitric oxide for inhalation. A multi-center study is necessary to recruit an appropriate number of subjects, and to reflect the variability of standard practice across the different participating centers. All treatment assignments are blinded in order to minimize the risk of bias in treatment and data collection. In addition, a concurrent placebo group has been chosen as the most appropriate control group since there may be temporal, institutional and national variations in average outcomes. Methemoglobin levels will be measured locally and will collected in a blinded manner.