Fibrosing alveolitis (FA) is a frequent and often fatal complication of systemic sclerosis (SSC). Alveolar inflammation has been recognized as a primary event in the pulmonary manifestation of SSC. To evaluate the significance of the alveolitis in SSC, we performed bronchoalveolar lavage (BAL) and correlated the generated data with changes in lung function over time. Seventy nine SSC patients with pulmonary involvement were followed for 56.8 +/- 3.1 wk (mean +/- SEM) with a repeat lung function test at the end of the follow-up period. During follow-up, 38 patients were treated with a systemic immunosuppressive regimen. For evaluation, patients were assigned to two groups according to whether their BAL cell differential was normal (inactive BAL) or abnormal (active BAL: i.e., polymorphonuclear leukocytes > 5% and/or lymphocytes > 15%). Active BAL was associated with more severe lung function impairment than was inactive BAL, and patients with active BAL deteriorated during follow-up if untreated. In contrast, treated patients with active BAL stabilized or improved. In summary, active alveolitis as characterized by BAL is associated with progressive pulmonary disease in SSC patients, and a significant positive effect of immunosuppressive therapy on the course of pulmonary disease was observed in patients with active BAL.