Eight neutralizing and two non-neutralizing antifoot-and-mouth disease virus (FMDV) bovine IgG1 and IgG2 monoclonal antibodies (BMAbs) recognize conformationally dependent epitopes. The majority of those shown to neutralize virus passively protected mice from virus challenge, regardless of isotype. Well-characterized anti-FMDV mouse MAbs, representing five independent neutralizing epitopes on O 1 serotype virus, were examined with each of the ten BMAbs in a competition-based ELISA. Five of the neutralizing BMAbs (C48, C65, C74, C83 and MH6) were shown to be directed against epitopes on, or in close proximity to, that previously defined as neutralizing antigenic site 2. Another neutralizing BMAb, MH5, bound to an epitope on, or in close proximity to antigenic site 3. Two neutralizing BMAbs (C2 and C96) simultaneously