Mobile genetic elements are useful genetic tools. They have been found in most organisms which have been examined (for recent reviews see 1). /S900 was isolated from M. paratuberculosis (2) and IS6100 from a M. fortuitum strain (our unpublished results). IS elements have been used as taxonomic markers useful for diagnostic purposes, (2, 3). From a IA. tuberculosis cosmid library constructed in pHC79 (4), an IS-like element, 1S6110, was identified as a repeated sequence, by screening the library with labelled M. tuberculosis total DNA. This sequence (1361 nt) possesses characteristics of IS elements, i.e., inverted (28bp with 3 mismatched bp) and direct (3bp) repeats of the target sequence at its extremities. A search in the EMBL data bank has revealed homologies with IS3411, an insertion element from E. coli (5). Cross-hybridization was observed between 1S6110 and a repeated sequence previously isolated from M. tuberculosis (6). IS6110 has been found in M. tuberculosis and M. bovis but not in any of the other mycobacteria tested (our unpublished data). Therefore, IS6110 will be used as probe for the identification of the M. tuberculosis complex. ACKNOWLEDGEMENTS