Hypoxemic respiratory failure in the newborn (NHRF) is usually associated with widespread vasoconstriction of the pulmonary microvasculature giving rise to intra- and extra-pulmonary shunts and profound hypoxemia. The goal of therapy is to decrease the regional pulmonary vascular resistance of ventilated lung areas thus decreasing intrapulmonary shunting and selectively reducing the pulmonary-artery pressure without causing systemic vasodilation. Intravenously administered vasodilators lack pulmonary selectivity leading to systemic side effects. Inhaled nitric oxide (INO), a selective pulmonary vasodilator, has revolutionized the treatment of respiratory failure in the newborn. However, there is lack of sustained improvement in 30-46% of infants; moreover, INO requires specialized systems for administration, making the treatment expensive. Aerosolized prostaglandins I2 and E1 have been reported to be effective selective pulmonary vasodilators in animals and human adults. In addition, inhaled prostaglandin I2 (IPGI2) has also been reported to be effective in preterm and term newborns, and children with pulmonary hypertension. Although intravenous PGE1 is widely used in neonates, the use of the inhaled form has not been reported in newborns with pulmonary hypertension. Compared to PGI2, PGE1 has a shorter half-life, lower acidity constant (pKa) (6.3 versus 10.5), bronchodilator action, anti-proliferative and anti-inflammatory effects on the alveolar, interstitial and vascular spaces of the lung. Prostaglandin nebulization can be used without the sophisticated technical equipment needed for controlled NO inhalation and hence is less expensive. It has no known toxic metabolites or toxic effects. Prostaglandins and nitric oxide (NO) relax the vascular smooth muscles through two different second-messenger systems; therefore, in combination, INO and IPGE1 may have synergistic effect. The existing literature suggests that inhaled PGE1 is a potential effective vasodilator in the treatment of NHRF . We have reported the safety and feasibility of short-term administration of inhaled PGE1 in an un-blinded Phase I/II dose-escalation study. Four doses ranging from 25 to 300 ng/kg/min were tested for a maximum duration of 3 hours. We have also reported the stability of IPGE1, its emitted dose and aerosol particle size distribution (APSD) in a neonatal ventilator circuit. In addition we have demonstrated the safety of high dose IPGE1 (1200 ng/kg/min) over 24 hours in ventilated piglets. In the current protocol, we propose a pilot to evaluate the feasibility and safety of prolonged IPGE1 in NHRF. Two doses of IPGE1 (300 and 150 ng/kg/min) will be tested followed by weaning for a maximum duration of 72 hours to determine feasibility, safety, optimal dose and duration of therapy in 50 patients in ten NICHD NRN sites. An IND status has been approved by the FDA for this trial.