Pulmonary hypertension can occur primarily with an unknown aetiology or secondary in association with cardiac or pulmonary disorders such as congenital diaphragmatic hernia, idiopathic respiratory distress syndrome, acute respiratory distress syndrome (ARDS), congenital heart disease with malformation of the pulmonary blood vessels, chronic obstructive lung disease and following cardiac surgery. Prostacyclin (PGI(2)), an arachidonic acid metabolite, has been evaluated for its efficacy in the treatment of pulmonary hypertension and for its use in assessing the reversibility of the disorder prior to surgical interventions. While the intravenous application of PGI(2) can cause a decrease not only of the pulmonary but also of the systemic vascular tone, aerosolised PGI(2) results in a selective pulmonary vasodilation without affecting the systemic blood pressure. Furthermore, aerosolised PGI(2) can improve gas exchange and pulmonary shunt in clinical settings of impaired ventilation/perfusion ratio such as ARDS, due to the redistribution of pulmonary blood flow from nonventilated to ventilated, aerosol-accessible lung regions.Aerosolised prostacyclin can be a valuable tool in the treatment and diagnostic evaluation of elevated pulmonary vascular resistance and impaired pulmonary gas exchange. Reservations must be made for its long-term use, as its short half-life necessitates continuous inhalation.