The coding sequence for the Digitalis lanata EHRH. cardenolide 16'-O-glucohydrolase was inserted downstream of the 35S promoter in the binary vector pBI121 resulting in plant expression vector pBI121cgh. Cotyledon explants excised from 10-day-old seedlings of Cucumis sativus L. were transformed using Agrobacterium rhizogenes 15834 harbouring pBI121cgh. Hairy roots were obtained from infected cotyledon explants in vitro 10 days after inoculation. PCR amplification of coding sequences for cgh I, rolB and rolC from Ri plasmid showed that the aimed sequences were inserted into the genome of transformed cucumber hairy roots. Glycolytic activity of the transgenic CGH I was measured by HPLC using Lanatoside glycosides as substrate. Therefore, the cgh I transformed cucumber hairy roots may provide a valuable model for biotransformation of natural compounds by recombinant enzymes.