The recognition of homocytotropic antibodies and their occurrence in response to parasite infection preceded the recognition of IgE as a distinct antibody isotype in the bovine species. Passive cutaneous anaphylaxis was an early reliable and antigen specific method to detect IgE in bovine serum. Yet studies on the role of IgE in bovine disease awaited the production of polyclonal and monoclonal antisera specific for the bovine epsilon chain. Applications of antigen specific ELISA and Western blot techniques have demonstrated IgE responses not only to parasite antigens, but also to viral and bacterial pathogens. The role of IgE in vaccine enhanced disease and in eliciting anaphylactic responses to some vaccines has been elucidated using these immunological assays.