[en] Three new insertion elements, IS Mbov1, ISMbov2 and ISMbov3, which are closely related to ISMag1 (Mycoplasma agalactiae), ISMmy1 and IS1634 (both Mycoplasma in mycoides subsp. in mycoides SC), respectively, have been discovered in Mycoplasma bovis, an important pathogen of cattle. Southern blotting showed that the genome of M. bovis harbours 6-12 copies of ISMbov1, 11-15 copies of ISMbov2 and 4-10 copies of ISMbov3, depending on the strain. A fourth insertion element, the IS30-like element, is present in 4-8 copies. This high number of IS elements in AI bovis, which represent a substantial part of its genome, and their relatedness with IS elements of both M. agalactiae and M. mycoides subsp. mycoides SC suggest the occurrence of two evolutionary events: (i) a divergent evolution into ill. agalactiae and M. bovis upon infection of different hosts; (ii) a horizontal transfer of IS elements during co-infection with M. mycoides subsp. mycoides SC and Ad. bovis of a same bovine host. (c) 2005 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.