BUILD 3: Bosentan Use in Interstitial Lung Disease

Inclusion Criteria: * Signed informed consent * Male or female aged 18 years or older (females of child-bearing potential must have been surgically sterilized or use a reliable method of contraception.) * Proven diagnosis of IPF according to American Thoracic Society / European Respiratory Society (ATS-ERS) statement, of \<3 years, with surgical lung biopsy (SLB) Exclusion Criteria: * Interstitial lung disease due to conditions other than IPF. * Presence of extensive honeycombing (HC) on baseline high-resolution computed tomography (HRCT) scan. * Severe concomitant illness limiting life expectancy (\<1 year). * Severe restrictive lung disease. * Obstructive lung disease. * Diffusing capacity of the lung for carbon monoxide \<30% predicted. * Residual volume \> or = 120% predicted. * Documented sustained improvement of patient's IPF condition up to 12 months prior to randomization with or without IPF-specific therapy. * Recent pulmonary or upper respiratory tract infection (up to 4 weeks prior to randomization). * Acute or chronic impairment (other than dyspnea) limiting the ability to comply with study requirements. * Chronic heart failure with New York Heart Association (NYHA) class III/IV or known left ventricular ejection fraction \<25%. * Alanine aminotransferase (ALT/SGPT) and/or aspartate aminotransferase (AST/SGOT) \> 1.5 times the upper limit of the normal ranges. * Moderate to severe hepatic impairment. * Serum creatinine \> or = 2.5 mg/dl or chronic dialysis. * Hemoglobin concentration \<75% the lower limit of the normal ranges. * Systolic blood pressure \<85 mmHg. * Pregnancy or breast-feeding. * Current drug or alcohol dependence. * Chronic treatment with the following drugs prescribed for IPF (within 4 weeks of randomization):oral corticosteroids (\>20 mg/day of prednisone or equivalent), immunosuppressive or cytotoxic drugs, antifibrotic drugs, chronic use of N-acetylcysteine (prescribed for IPF). * Oral anticoagulants other than those indicated for a venous or arterial thrombotic disease. * Treatment with glibenclamide (glyburide) and calcineurin inhibitors (cyclosporine A, tacrolimus) up to 1 week prior to randomization. * Treatment with an endothelin receptor antagonist up to 3 months prior to randomization. * Participation in the BUILD 1 trial. * Treatment with another investigational drug up to 3 months prior to randomization or planned treatment. * Known hypersensitivity to bosentan or any of the excipients.