The use of selective pulmonary vasodilators or vasoconstrictors is a new therapeutic option to improve arterial oxygenation in patients with ARDS. The objective of such a therapy is to reduce the need for high 02 concentrations and airway pressures, thereby decreasing ventilator-induced lung injury. Nitric oxide (NO) is one part of this approach. It is administered through the inhalation route in mechanically ventilated patients. It reduces the vasomotor tone of pulmonary vessels from the ventilated part of the lung. It also reduces pulmonary arterial pressure and alveolar deadspace. Aerosolized prostacyclin in doses as low as 2ng/kg/1/min is another means to improve arterial oxygenation, through a dilation of the vessels located in the ventilated part of the lung. Conversely, almitrine improves arterial oxygenation by reinforcing hypoxic pulmonary vasocon-striction. When combined with inhaled NO, the benefical effect of almitrine on arterial oxygenation is potentiated while its detrimental effects on the pulmonary circulation are blunted. Cyclooxygenase inhibitors also improve arterial oxygenation byr einforcing hypoxic pulmonary vasoconstriction. All these new treatments have profoundly changed the therapeutic strategy aimed at correcting life-threatening hypoxemia in patients with severe acute respiratory distress syndrome.