Lung macrophages may play a relevant role in oxidative processes producing both superoxide anion (O(2)(-)) and NO. In this view, an antioxidant therapy can be useful in the treatment of systemic sclerosis (SSc) patients. N-Acetylcysteine (NAC) is able to expand natural antioxidant defenses by increasing intracellular gluthatione concentration and it has been proposed as an antioxidant therapy in respiratory distress syndromes. The aim of our study was to determine whether lung macrophages obtained from SSc patient bronchoalveolar lavage (BAL) express the inducible form of nitric oxide synthase (iNOS) and whether NAC can reduce the peroxynitrite (ONOO(-)) and O(2)(-) production of these cells. Alveolar macrophages were isolated from BAL of 32 patients and used for the immunocytochemical determination of iNOS, and the production of ONOO(-) and O(2)(-) was measured by fluorimetric or spectrophotometric methods, respectively. Lung macrophages obtained from SSc patients expressed a higher level of iNOS compared to healthy subject cells. NAC preincubation (5 x 10(-5)M, 24h) significantly reduced (-21%) the ONOO(-) production in formyl Met-Leu-Phe (fMLP)-activated cells and slightly reduced it under resting conditions, whereas NAC preincubation was unable to modify the release of O(2)(-) both in basal condition and in fMLP-stimulated cells. We conclude that since SSc lung macrophages express high levels of iNOS and produce a significant quantity of ONOO(-), NAC administration reduces ONOO(-) production and can be an useful treatment to alleviate SSc symptoms.