The combination of inhaled nitric oxide with almitrine bismesylate has been proposed for the management of acute respiratory distress syndrome in order to divert pulmonary blood flow away from poorly ventilated toward well-ventilated areas. The aims of this prospective and comparative study were to: 1) confirm the beneficial effects on oxygenation of this association; 2) evaluate the haemodynamic effects of this association; and 3) evaluate the influence of noradrenaline (a nonspecific vasoconstrictor) on the modification of gas exchange related to inhaled NO and/or almitrine bismesylate. Forty-one sedated paralysed and ventilated patients were investigated. Haemodynamic and blood gas measurements were performed in a fixed order: baseline; inhalation of NO for 30 min.; intravenous infusion of almitrine bismesylate; and concomitant administration of inhaled NO and almitrine bismesylate. Inhaled NO and almitrine bismesylate increased arterial oxygen tension (Pa,O2)/inspiratory oxygen fraction (FI,O2) (p<0.001). The association of inhaled NO with almitrine bismesylate resulted in a dramatic improvement in Pa,O2/FI,O2 (p<0.0001 versus almitrine bismesylate, p<0.05 versus inhaled NO). In patients receiving noradrenalin (n = 19), almitrine bismesylate had no effect on oxygenation. The present study confirmed that the combination of inhaled NO with almitrine bismesylate improved oxygenation, and demonstrated that almitrine bismesylate has no effect on oxygenation in patients receiving noradrenalin.