Conditions were optimized for transient transformation of Lilium longiflorum 'Nellie White' using Agrobacterium tumefaciens. Bulb scale and basal meristem explants were inoculated with A. tumefaciens strain AGL1 containing the binary vector pCAMBIA 2301 which has the uidA gene that codes for beta-glucuronidase, GUS expression. Transformed bulb scales showed transient GUS expression when they had been precultured 11 days on Murashige and Skoog's (MS) medium supplemented with 2 mg/L dicamba. The outer, larger-sized bulb scales were not infected nearly as well as the inner, smaller bulb scales. Maximum GUS expression occurred when bulb scales had been obtained from plants that had been grown in the dark for at least 2 months rather than in the light indicating the importance of growing plants in the dark for Agrobacterium-mediated transient transformation of bulb scales. Basal meristems taken from plants grown 4 months in the dark showed 3 times as much GUS expression as basal meristems from plants grown in a 12 h light photoperiod. The frequency of transient GUS expression achieved in this study indicated that it should be possible to achieve stable transformation of 'Nellie White' which is the cultivar that dominates the US market of Easter lilies. Experiments for stable transformation are in progress.