SUMMARY. Introduction: Idiopathic pulmonary fibrosis (IPF) is characterized by progressive deterioration of lung function, leading ultimately to death. No pharmacological treatment has been found to stabilize the evolution of the disease, but interferon-g and azathioprine have been used as therapeutic options. Aim: To compare the effectiveness of treatment with interferon-g plus low dose prednisone or azathioprine plus low dose prednisone in patients with IPF. Materials and methods: Patients newly diagnosed with IPF were recruited, 22 in total, of whom 10 received azathioprine plus prednisone and 12 patients received interferon-g plus prednisone for six months. Clinical evaluation, lung function tests, HRCT, bronchoscopy and bronchoalveolar lavage (BAL) were performed at baseline and after six months of treatment. Results: All patients were alive after six months of treatment. No statistically significant difference between the two groups was detected regarding clinical deterioration, inflammatory biomarkers such as erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and BAL cell sub-populations. There was a trend, not statistically significant, towards a greater reduction in forced vital capacity and diffusing capacity for carbon monoxide in the interferon-g group. Conclusion: Interferon-g does not offer any therapeutic advantage over azathioprine as regards the clinical course, lung function tests and BAL cell counts of patients with IPF. Pneumon 2009, 22(3):247-253.