This study aimed at evaluating acute pulmonary remodeling, focusing on alterations of fibers of the collagenous and elastic systems in ARDS in the exudative phase according to the etiology of the disease. ARDS patients (n = 23), who died in our institution between 1989 and 1997, were retrospectively studied. Ten patients who died in accidents, without any pathological changes in the lung, and ten patients with Congestive Heart Failure (CHF), submitted to mechanical ventilation, were used as control groups. Histological slides were sampled from the autopsied lungs and stained by the Picrosirius and Weigert's resorcin-fuchsin methods. The fiber content of the collagenous and elastic systems of the alveolar septum was measured by image analysis. All patients were in the early ARDS phase (n = 23), 10 pulmonary and 13 extra-pulmonary diseases. Collagen content was greater in pulmonary (1.23+/-0.27) than in extra-pulmonary (0.92+/-0.39) ARDS in the early phase of the disease (p = 0.05). No differences were observed concerning the elastic fibers' content. Extracellular matrix (ECM) remodeling occurs early in the development of acute lung injury and appears to depend on the site of initial insult (pulmonary or extrapulmonary). The present study provides the basis for a prospective, controlled investigation.