A lveolar macrophages (AMs) recovered from the bronchoalveolar lavage (BAL) of 44 patients with sarcoidosis were evaluated for their ability to release type IV collagenolytic metalloproteinase (IV-Case). This enzyme, which is produced by peripheral blood monocytes (PBMs) but not by tissue macrophages, degrades type IV collagen, the major structural component of vessel wall basement membranes, and helps to promote the migration of PBMs from the blood compartment to peripheral tissues. Our results demonstrated that AMs from patients with active sarcoidosis released significantly increased levels of IV-Case with respect to patients with inactive disease and control subjects. After in vitro culture, sarcoid AMs secreted IV-Case during the first 24 h of collection; after that time, AMs progressively lost their ability to release IV-Case. Exposition of both sarcoid and normal AMs to recombinant IL 2 or gamma IFN did not influence their property to release IV-Case. The immunoblot analysis of IV-Case demonstrated complete identity between IV-Case released by AMs and the degradative enzyme obtained from PBMs. The increased property to release IV-Case was significantly related to the increase of the absolute number of AMs and, in particular, of AMs bearing two determinants that are usually expressed by most PBMs (CD11b and CD14). Selective depletion of CD11b+/CD14+ AMs from the entire macrophagic population was associated with the recovery of the IV-Case activity to normal values. A positive correlation was also found between the increase in the absolute number of lung T cells and the enhanced CD4/CD8 pulmonary ratio. A 6-mo follow-up study indicated a significant association between the positivity for the 67Gallium scan and the increased property of AMs to release IV-Case. Our data are consistent with the hypothesis that a IV-Case mediated influx of peripheral monocytes takes place in the lung of sarcoid patients. Furthermore, the correlation found between the IV-Case release and disease activity suggests that this assay could represent a useful tool in sarcoidosis disease staging.