BACKGROUND Patients with the adult respiratory distress syndrome (ARDS) present a deficit of tissue oxygenation which may be unmasked if increases in oxygen uptake (VO2) are observed when increases in oxygen delivery (DO2) are induced. Prostacyclin is a drug to which microvasodilator effects have been attributed and it has been proposed as an efficient agent for increasing histic enhancement of oxygen. METHODS An infusion of prostacyclin was administered to 13 patients diagnosed with ARDS at doses of 10, 20, and 30 ng/kg per minute monitored with a Swan-Gatz catheter. RESULTS The values are expressed as the percentage median of the increase with p less than 0.05 being considered as statistically significant. Prostacyclin significantly increased DO2 (10, 18 and 15% at the different doses). The VO2 rose significantly only following the first dose (13%). There was a correlation between the increase of DO2 and that of VO2 following the administration of the first dose (r = 0.70, p = 0.017. An important systemic vasodilator and pulmonary effect was observed accompanied by increases in the pulmonary (20, 56 and 59%) and reductions of PaO2 (-33.5, -40 and -48%) which may have been due to inhibition of hypoxic vasoconstriction. CONCLUSIONS Prostacyclin is efficient for unmasking a lack of oxygen in patients with adult respiratory distress syndrome. The deleterious effects of this drug on systemic hemodynamics and on gaseous interchange makes not only the monitorization of arterial pressure but also of the parameters of gaseous interchanges necessary in these patients.