Spleen cells from Balb/c mice immunized with purified rat plasma kininogen were fused to P-3 mouse myeloma cells. Positive clones were identified by enzyme linked immunosorbent assay (ELISA), cloned successively two times with limiting dilution and expanded as ascites tumors. Five hybridomas were developed that produced monoclonal antibodies against plasma kininogen. Two of the secreted antibodies were of the IgG1 (k) isotype and the remaining three were of the IgG1(lambda), IgG2A(k) and IgM(k) isotypes respectively. The specificity of the monoclonal antibodies was confirmed by the immunoprecipitation of kininogen with the antibodies coupled to Sepharose-4B followed by SDS-polyacrylamide gel electrophoresis. These monoclonal antibodies recognize at least two distinct epitopes on rat plasma kininogen.