Abstract: Agrobacterium-mediated plant genetic transformation requires a two-step process for its success: selection and regeneration of transformed tissues, and the elimination of the transformation vector, Agrobacterium. This study uses carbenicillin (CA), cefotaxime (CF) and vancomycin (VA) singly, or in combination, to eliminate Agrobacterium tumefaciens LBA4404 and AGLO growing on Agrobacterium-favouring (LB) and plant-favouring (MS) media, at transgenic plant selection levels (10 or 25 micro g/ml kanamycin for chrysanthemum and tobacco, respectively). The three antibiotics differed in their capacities to eliminate Agrobacterium i.e., bacterial threshold survival levels (TSLs), depending on the strain, medium and light conditions. Plant TSLs differed from those for Agrobacterium, and were cultivar-, species- and light-dependent, with CA > VA > CF in terms of phytotoxicity. Since over 90% of plant transformation experiments use Agrobacterium as the transformation vector, with most of these containing an aminoglycos