Two monoclonal antibodies that recognize bovine tissue factor (coagulation factor III) were obtained following the fusion of hyperimmune mouse spleen cells with Ns-1 plasmacytoma cells. Both antibodies, TF1-E2 and TF1-F7, have .gamma.1 H chains and .lambda. L chains, TF1-E2 and TF1-F7 have each been used to purify bovine tissue factor from a crude detergent extract of bovine brain by immunoaffinity chromotography. both antibodies inhibit tissue factor procoagulant activity and block the association of factor VIIa with tissue factor. The association of TF1-F7 and tissue factor solubilized in Triton X-100 was measured under equilibrium conditions. The Kd for this antibody-antigen interaction with 2.1 .+-. 0.2 nmol/l. TF1-E2 effectively competes with TF1-F7 for tissue factor binding, indicating that the monoclonal antibodies recognize overlapping sites on the protein. These antibodies will be useful reagents for large-scale purification and for structure-function studies of bovine tissue factor. In particular, since they appear to bind to the same region of the tissue factor molecule as factor VIIa, they will be useful as specific probes for studying the kinetics of tissue factor-initiated coagulation and for immunocytochemical localization of tissue factor in bovine cells.