Corynebacterium pseudotuberculosis is a bacterium that infects horses and many large animal species worldwide. Infections of the bacteria cause ?Dryland Distemper? or ?Pigeon Fever?, characterized by large external abscesses on the pectoral and abdominal region of horses. Phospholipase D (PLD) is the main antigen and exotoxin (protein) produced by C. pseudotuberculosis , and causes many of the symptoms associated with the infection. PLD protein was isolated and/or purified from peanut, cabbage, and recombinant E. coli containing the PLD gene. The major question of the study is whether infected or uninfected horse sera has IgG antibodies that cross react or have some specificity for the different PLD antigens. There was noticeable cross reactivity against the peanut and cabbage PLD confirmed by ELISA using the Horse Radish Peroxidase system; however, the Alkaline Phosphatase system showed little to no cross reactivity. It is hypothesized that the HRP system may be a much more sensitive assay. Lastly, bacterial cultures of Equine C. pseudotuberculosis , Ovine C. pseudotuberculosis , and C. ulcerans were grown and their purified and concentrated supernatants as well as their whole cell lysates were tested against different horse sera by western blot to determine whether infected horse sera reacts with different bacterial strains with high PLD sequence homology. Characterizing the PLD antigen for homology among different species and cross reactive antibody interactions will help us better understand the pathology of this disease.