Intravascular infection with Staphylococcus aureus, Staphylococcus epidermidis, or Streptococcus sanguis can initiate fibrin formation on endocardial tissue, causing bacterial endocarditis. The ability of these bacteria to injure intact endothelial cells (ECs) and to aggravate tissue factor (TF)-dependent coagulation in the presence of blood leukocytes was investigated. Cytolysis of ECs occurred after infection with S. aureus and, with membrane-bound monocytes or granulocytes present, also after infection with S. sanguis or S. epidermidis. Monocytes that subsequently bound to the resultant bacteria-infected subcellular EC matrix (ECM) elicited TF mRNA, TF antigen, and TF activity (TFA). This was most pronounced in ECM prepared after the cytolysis of ECs by infection with S. aureus or S. epidermidis. We demonstrate that monocytes continue and intensify fibrin formation after lysis of bacteria-infected ECs, which suggests that, during the course of intravascular infection, early fibrin formation shifts from being mediated by EC-derived TFA to being mediated by TFA of monocytes bound to bacteria-infected ECM.