Idiopathic pulmonary fibrosis (IPF) is a quality-of-life-altering and life-shortening lung disease manifested by physiologic restriction, hypoxemia and progressive shortness of breath. Despite nearly 30 years of investigation, the median survival for patients with this disease remains dismal at approximately 3 years from the time of diagnosis. Recent investigations have identified a number of potential molecular therapeutic targets for IPF that include endothelin-1 and other fibrogenic cytokines. Bosentan, a nonselective endothelin receptor antagonist approved in the USA and Europe for the treatment of patients with pulmonary arterial hypertension, is currently undergoing evaluation as a potential therapy for IPF. A recently completed multinational, placebo-controlled trial failed to show a beneficial impact of bosentan on the primary end point, but results from a hypothesis-generating, post hoc analysis of data from this trial have prompted an assessment of the drug for efficacy in a selected subgroup of IPF patients – those with biopsy-proven IPF and little radiographic honeycombing. Results from this trial are anticipated in 2009.