Summary. Fertile and stable transgenic plants of the model legume Medicago truncatula Gaertn. were obtained through transformation of leaf tissue with the disarmed Agrobacterium tumefaciens strain LB4404 and in vitro regeneration via somatic embryogenesis. An optimised transformation/regeneration protocol has been established for two genotypes of the cultivar Jemalong, including a previously described highly embryogenic line (Nolan et al. 1989, Plant Cell Rep. 8: 278-281). Using this protocol, transgenic plantlets were obtained within 4-10 months following cocultivation with Agrobacterium. We have introduced into M. truncatula a chimeric fusion between the early nodulin MtENOD12 promoter and the gus (ß-glucuronidase) reporter gene, and shown that symbiosis-specific gene expression can be elicited in the roots of such transgenic plants following the addition of purified Rhizobium nodulation factors.