The multi-center, controlled and blinded trial investigates the hypothesis that low-dose inhaled nitric oxide administered to preterm infants between 500 and 1250 grams birth weight who continue to require mechanical ventilation at 10 days of age will increase survival without chronic lung disease (CLD) at 36 weeks post menstrual age. Secondary outcomes are duration of ventilation, oxygen requirement and duration of hospitalization. In addition, that there will be expected improvement in infant respiratory status (ventilatory support, airway resistance and compliance) associated with inhaled nitric oxide treatment. Indicators of inflammation and oxidant stress will be assessed by measurements of specific cytokines and protein modifications in tracheal aspirate and plasma samples, respectively. The safety of this therapy will be evaluated by assessing toxicity as measured by clinical bleeding, including intraventricular hemorrhage as well as the incidence of other morbidities of the preterm infant (necrotizing enterocolitis, retinopathy of prematurity and infection) and assessing neurodevelopmental outcome through two years of age. A total of 480 infants were randomized to either inhaled NO or placebo. In summary, this clinical trial will assess the efficacy and safety of inhaled nitric oxide for amelioration of a major disease of premature infants.