Idiopathic pulmonary fibrosis (IPF) is now recognized as a separate nosological entity. Despite the progresses in understanding the basic mechanisms of the disease, its prognosis remains poor. The classical treatment combines prednisone with a cytotoxic agent. Interferon gamma has the in vitro capacity of inhibiting fibroblasts proliferation. A pilot study showed positive results, but a more recent randomized double blind trial was unable to demonstrate a clear benefit to the patients. On the other hand there are many evidences for an oxydant-antioxydant imbalance in the pathogenesis of IPF. In a human controlled study N-acetylcysteine (NAC) at high doses (1800 mg per day orally) improved the pulmonary function tests when given on top of a combined therapy with prednisone and azathioprine.