The eradication of bovine tuberculosis is an ultimate aim of the beef industry and the development of accurate diagnostic tests will expedite eradication. Characterization of Mycobacterium bovis antigens, and a detailed understanding of their immune reactivity will aid in the development of more specific and sensitive diagnostic tests. With this aim, studies were conducted which have resulted in the purification and immunological characterization of the major soluble M. bovis antigens. The purified antigens were found to contain cross-reactive epitopes and immunological responses to these proteins varied among individual animals. Thus if more specific diagnostic tests are to be formulated, they will have to be at the epitope level, using only species-specific epitopes and not whole proteins. Due to the genetic diversity of the response of infected cattle to individual epitopes, a large cocktail of such epitopes will be necessary for the development of a sensitive test.