Tissue factor (TF) mRNA levels in leukocyte and TF antigen in plasma were examined in patients with deep vein thrombosis (DVT). Although TF mRNA levels in leukocytes were higher in patients with DVT than in healthy volunteers, they were lower in patients with DVT than in those with solid cancer and those with disseminated intravascular coagulation (DIC). On the other hand, the plasma levels of TF antigens were markedly high in patients with DVT/pulmonary embolism (PE). Analysis of the role of underlying disease of DVT showed no significant difference in TF mRNA levels and TF antigens among patients with solid cancer, post-surgical, other diseases and those free of underlying diseases. In patients with VTE, plasma levels of D-dimer, soluble fibrin, GE-XDP and plasminogen activator inhibitor-1 did not correlate with TF mRNA or TF antigen. In analysis of 18 patients with PE with and without DVT, TF mRNA levels in leukocytes correlated with the plasma levels of D-dimer. These findings suggest that TF in leukocytes is more likely to be involved in the development of thrombosis in PE than DVT.