Herein we report on developmental changes of pulmonary and systemic nitric oxide metabolites in a baboon model of chronic lung disease with or without exposure to inhaled nitric oxide. The plasma levels of nitrite and nitrate, staining for S-nitrosothiols and 3-nitrotyrosine in the large airways increased between 125 days and 140 days of gestation (term 185 days) in animals developing in utero. The developmental increase in nitric oxide-mediated protein modifications was not interrupted by delivery at 125 days of gestation and mechanical ventilation for 14 days, while plasma nitrite and nitrate levels increased in this model. Exposure to inhaled nitric oxide resulted in a further increase in plasma nitrite and nitrate and an increase in plasma S-nitrosothiols, without altering lung NO synthase expression. These data demonstrate a developmental progression in levels of pulmonary nitric oxide metabolites that parallel known maturational increases in total NOS activity in the lung. Interestingly, despite known suppression of total pulmonary NOS activity in the chronic lung disease model, pulmonary and systemic nitric oxide metabolite levels are higher than in the developmental controls. Thus, a deficiency in nitric oxide production and biological function in the premature baboon was not apparent by the detection and quantification of these surrogate markers of nitric oxide production.