Hypoxia-related pulmonary vasoconstriction enhanced by norepinephrine could be deleterious in patients with the acute respiratory distress syndrome (ARDS) and sepsis. A prospective study compared the effects of nitric oxide on cardiorespiratory parameters, including the evaluation of right ventricular function in patients with ARDS and sepsis who were receiving or not receiving norepinephrine. During a 15-month period, 27 patients with ARDS and sepsis were prospectively investigated (group 1: 15 patients not receiving norepinephrine; group 2: 12 patients receiving norepinephrine). Right ventricular ejection fraction was measured by thermodilution. After baseline measurements, nitric oxide was administered at increasing inspiratory concentrations. The ratio of oxygen tension in arterial blood to the fractional concentration of oxygen in inspired gas increased in the two groups. After logarithmic transformation of the data, an analysis of variance was performed that did not show any difference between the two groups. A dose-dependent decrease in mean pulmonary arterial pressure was observed in the two groups. This decrease and the increase in right ventricular ejection fraction induced by inhaled nitric oxide were more marked when patients received norepinephrine (P < 0.0001). Norepinephrine did not influence the beneficial effects of inhaled nitric oxide administered to patients with ARDS and sepsis on oxygenation.