A mouse hybridoma HS@03A secreting anti-horseradish peroxidase (HRPO) monoclonal antibodies (IgG1) was established. A HAT sensitive clone of HS@03A was obtained by culturing the hybridoma cells in a 6thioguanine supplemented medium. The resulting clone 03AR10-2 was fused with a 5-bromo-2'-deoxyuridine resistant (HAT sensitive) clone of a mouse hybridoma HB8852 secreting anO-bovine lactoferrin (bLF) antibodies. Hybridhybridomas secreting bispecific antibodies were selected and a hybridhybridoma clone HH1-4-3 was established. The bispecific antibodies secreted by the hybrid-hybridoma HH1-4-3 were found to be useful for the analysis of bLF by competitive ELISA.