The Eurasian badger (Meles meles) is a significant wildlife reservoir of Mycobacterium bovis in Great Britain. Improved control strategies against the disease in badgers require the development of diagnostic tests and vaccines. Here, we report the development of a comparative lymphocyte transformation assay (LTA) using bovine and avian tuberculin as antigen to detect cell-mediated responses in M. bovis-infected badgers. In a pilot study, the performance of this assay was compared with the existing indirect ELISA assay for the detection of tuberculous badgers. The sensitivity of the Comparative LTA was 87.5% compared with 62.5% for the indirect ELISA whereas the ELISA test gave a greater specificity (100% compared with 84.6% for the comparative LTA). Preliminary evidence suggests that for the comparative LTA, the blood may be stored overnight prior to testing and that this procedure might improve the specificity of the assay without compromising the sensitivity.