b-glucuronidase (GUS) and neomycin phosphotransferase II (NPTII). The gene is under the control of a double 35S Cauliflower Mosaic Virus promoter and a leader sequence from Alfalfa Mosaic Virus. The cells were placed on kanamycin-containing media (10, 25 or 50 mg/l) 2 days after bombardment. Activated charcoal in the media reduced cell browning. Embryos were first observed on selective media 14 to 29 weeks after bombardment. More than 1600 clusters of embryos were excised and germinated and/or assayed for GUS expression. Of the 621 embryos assayed for GUS expression, 182 (29.3%) were positive. PCR amplification confirmed the presence of the NPTII gene in all of the 5 GUS-positive and 2 GUS-negative embryos tested. In germination experiments, 15% of the embryo clusters produced at least one plant with normal shoot growth. Of the 164 normal plants assayed for GUS expression, 37 (22.6%) were positive. The NPTII gene was amplified by PCR in 1 (of 1) GUS-positive and 4 (of 5) GUS-negative bombarded plants, but not in non-bombarded control plants. Biolistics is an efficient method for genetic transformation of 'Chancellor' and should be applicable to other important grapevine cultivars.