In most cases, diagnosis of Marek's disease "MD" can be made on the basis of history, clinical signs and the presence of gross and microscopic lesions (Payne and Venugopal., 2000; Witter and Schat., 2003). However, in certain cases, additional tests e.g. immunohistochemistry using monoclonal antibodies are recommended. Being the replication in and shedding from feather follicle epithelium of complete Marek's disease virus (MDV), simple agar- gel diffusion test is employed, using an homogenate of feather follicles or more simply, the feather tips as antigen against an hyperimmune specific antiserum. The reaction antigen-antibody occurs in 24–36 hours of incubation at room temperature and is characterized by very marked precipitation line.