Direct evidence for the lack of intrinsic β-glucuronidase (GUS) gene in Agrobacterium tumefaciens LBA4404 was presented using PCR technique. No amplified fragment was obtained with a 21 bp primer pair, which is specific for the sequence of the GUS gene, from total cell DNA of the Agrobacterium tumefaciens LBA4404, whereas a single 1 .2 kb fragment, which is identical in size to that predicted for the internal GUS gene fragment,was amplified with the same primer pair from total cell DNA of the LBA4404 containing the plasmid pBI121 and from purified pBI121 respectively.