The technique of immunohistochemical staining allows the visualization of epitopes in situ in histological tissue sections. A series of innovations in the methods and reagents and the introduction of mechanization have enhanced the ease and technical reliability of this technique resulting in widespread application in veterinary diagnostics and research. This brief overview will highlight some of the applications for immunohistochemical staining with an emphasis on the use of the technique in diagnostic veterinary medicine, particularly for the detection of infectious disease agents.