Hepatitis C virus (HG ))infecrion has recenrly been incriminated as an aeriological agent in idiopathic p ulmonary fibrosis (IPF . This study was p erformed to study the cellularity of bronchoalveolar lavage (BAL)fluid and ventilatory function tests in patients with chronic HCV infecrion. BAL fluid and lavage from ten pa tienrs with chronic active hepariris C, diagnosed by elevated serum rmnsaminases and rypical histological findings in rhe li1•er. ll'ae analysed (group 1). Lavage findings and ventilatory fimc rions in rhese patienrs were compared with those from ren healthy volunteers as controls (group II). There was no difference in rota/ cell coums in rhe lavage fluid between the Mo g roups, but lavage lymphocyre and.eosinophil numbers were increased in chronic HCV patients. The ventilarory functions FVCo/o and FEV I % predicted and FEV /F VCo/o were significantly lower in the HCV pa tienrs (group 1). The FVC o/o, EFV 1o/o. FEF 15_75r, c pr edicted and FEV / FVCo/o were lower in rhe HCV p.arients with alveolitis. Thus, the numbers of lymphocytes and eosinophils in BAL fluid are increased in patients with chronic HCV. These findings suggest that chronic HCV infection may trigger alveolitis. This alveolitis may de­ crease rhe ventilatoryfimctions.