The N-terminal peptide of type III procollagen (PIIIP) and fibronectin (FBN), two markers possibly implicated in the pathogenesis of pulmonary fibrosis, were determined in bronchoalveolar lavage fluid (BAL) and in serum of 27 subjects with a history of occupational exposure to asbestos, in 10 sarcoidosis patients and in 7 healthy controls. At the same time, the study of the cell populations and asbestos bodies count in BAL were also performed. In BAL of sarcoidosis patients the mean concentration of PI-IIIP was higher compared to that of the other two groups, and the difference was significant compared with the healthy controls. Among the group of asbestos workers, both PIIIP and FBN were significantly higher in subjects with radiological signs of pulmonary asbestosis compared with those with no signs of asbestosis. On the basis of BAL cytology, the asbestos-exposed were divided into two subgroups, with or without signs of alveolitis: the mean concentrations of BAL PIIIP was significantly higher in the subgroup with alveolitis. Moreover, in this subgroup there was a positive correlation between total number of cells and PIIIP, and between the number of asbestos bodies and PIIIP in BAL. Serum PIIIP values did not differ significantly among the various groups, with the exception of higher values in sarcoidosis patients. The results of this study seem to confirm the usefulness of PIIIP and FBN determinations in BAL, as indicators of the activity of the fibrotic process which, in particular cases, might also assume a prognostic significance.