N-acetylcysteine (NAC), owing to its antioxidant, mucolytic and anti-inflammatory properties, is used in the treatment of various pulmonary disorders. However, the direct effects of NAC on bronchoalveolar lavage (BAL) cells from patients suffering from interstitial lung diseases have not yet been studied. Therefore, the aim of the present work was to evaluate the effect of NAC on interleukin-8 (IL-8) and matrix metalloproteinase-9 (MMP-9) production as well as intercellular cell adhesion molecule-1 (ICAM-1) expression by BAL cells from interstitial lung diseases. The study was performed on BAL cells from nine patients with interstitial lung disease: four patients with idiopathic pulmonary fibrosis (IPF) and five patients with sarcoidosis. Cultured unstimulated BAL cells were treated with increasing doses of NAC (1-30 mM). Production of IL-8 and MMP-9 was evaluated by specific enzyme-linked immuno-sorbent assays and ICAM-1 expression was studied by immunohistochemistry. NAC exerted a dose-dependent inhibitory effect on IL-8 and MMP-9 release and ICAM- expression by BAL macrophages and lymphocytes from patients with IPF and sarcoidosis. In conclusion, NAC inhibits production of factors playing a key role in the etiopathogenesis of interstitial lung diseases, thus suggesting its possible therapeutic potency in the treatment of these disorders.