The distribution patterns of endothelial cell antigens, including thrombomodulin and von Willebrand factor (vWf), were studied in normal lung tissues obtained from distant areas of solitary nodules (seven adenocarcinomas and four hamartomas). By single immunoalkaline phosphatase and dual immunofluorescence stainings, the plasma membranes of alveolar capillary endothelium showed linear distribution of thrombomodulin, but their cytoplasm was rarely reactive for vWf (thrombomodulin-dominant pattern). Microvessels with a diameter larger than 10 microm located in the connective tissue zones demonstrated band-like reaction for vWf in their cytoplasm, and their plasma membranes often lacked reactivity for thrombomodulin (vWf-dominant pattern). The juxta-alveolar microvessels located along the borders between the alveolar- and connective-tissue zones showed mosaic-like pattern of distribution for these antigens. The pulmonary venules and peribronchial microvessels measuring up to 40 microm in diameter, demonstrated the expression of thrombomodulin along the plasma membrane, and that of vWf in the cytoplasm. Capillaries of the bronchial circulation were also characterized by mosaic-like pattern of distribution. Both antigens were often expressed in a single cytoplasmic segment. The heterogeneous distribution pattern of these antigens suggests topographic difference in endothelial cell function to maintain coagulatory and anticoagulatory balance in the normal human lung.