Abnormalities in local coagulation may explain alveolar fibrin deposition which often accompanies human lung injuries. The purpose of this study was to investigate the generation of procoagulant activity (PCA) and tissue factor pathway inhibitor (TFPI) in selected bronchoalveolar lavage fluids (BAL) from controls (n = 7) and from patients with interstitial lung diseases (n = 9), Pneumocystis carinii (PCP) pneumonia (n = 11) and bacterial pneumonia (n = 8). As compared with controls a significant increase of PCA was observed in the three groups with lung diseases. PCA in BAL from patients with untreated interstitial lung diseases (PC Units mean of 162 +/- 48) was significantly higher than PCA of treated patients (PC Units 36 +/- 10; p less than 0.05). Increases of PCA paralleled protein levels in BAL and the protein/albumin ratios were comparable in the four groups. TFPI was significantly increased in PCP (p less than 0.02) and bacterial pneumonia (p less than 0.03), but only marginally increased in interstitial lung diseases when compared with controls. No correlation was found between TFPI and PCA in any of the four groups. These data indicate that increased procoagulant activity observed in various lung diseases is not counterbalanced by TFPI.