Bosentan (Tracleer, Actelion Pharmaceuticals Ltd) is an oral dual endothelin receptor antagonist approved for use in functional class III to IV pulmonary arterial hypertension. In two placebo-controlled trials, patients receiving bosentan showed improved functional class, 6-minute walk distance and hemodynamics over a 12- to 16-week period. Follow-up data over 3 years has shown few deteriorations,with the majority of patients maintaining their response to bosentan alone. Investigations exploring the use of bosentan as an add-on agent to intravenous epoprostenol (Flolan, GlaxoSmithKline Plc) in those with the most severe disease are ongoing. Bosentan may also have antifibrotic properties and its use in pulmonary fibrosis is being explored. Ease of administration of bosentan with twice-daily oral dosing will provide many patients with pulmonary hypertension an option for treatment without the risks and discomforts of continuous intravenous medication.