This study was conducted to detect the optimum conditions for DNA transfer into mature embryos of barley via electroporation. Cultured mature embryos of barley were directly electroporated in the presence of the pBI 121 vector carrying both the beta-glucuronidase (GUS) and neomycin phosphotransferase II (npt II) genes. It was found that 500 v/cm and 500 mu Fd capacitance was the optimum combination for healthy germination of the transformed plants from mature electroporated embryos. Effects of culture duration before electroporation and selection antibiotic concentrations on germination were also examined. Gene transfer performed on 3-day-old cultures resulted in the highest germination frequencies. GUS expression was observed on transversal sections of embryos and mature leaves from 3 month-old regenerants. PCR and Southern blot analyses show the presence of the npt II transgene in the genome of a plant.