Diagnosis of paratuberculosis is severely hampered by the lack of specific and sensitive diagnostic methods. In particular, serological tests are still of limited value partly because of cross-reactivity with related bacteria causing false positive reactions. The report on the immunodominance of a 34-kDa protein in sera of animals with Johne's disease promised the development of a new serological diagnostic tool. The more this new antigen contained species specific B-cell epitopes, facilitating the discrimination between infections with Mptb and related mycobacteria from the avium complex. In this study we showed that sera from quinee-pig infected with Ma recognized purified Mptb 34 kDa-antigen as well as a fusion-protein containing a C-terminal fragment of the 34 kDa-antigen containing "supposed Mptb specific" B-cell epitopes. We therefore conclude that claims on species-specific serological assay's based on the the 34 kDa antigen should be reconsidered.