SummaryA stable transformation system has been established in lavender (Lavandula latifolia Medicus) using Agrobacterium. Friable calli with high regeneration ability induced from leaf explant were infected with three strains of A. tumefaciens, and spread over the filter paper placed on the bacterial elimination medium containing 500 mg l–1 cefotaxime. After 7 d of culture, the filter paper with infected calli was transferred to the selection medium containing 50 mg l–1 hygromycin and 200 mg l–1 cefotaxime. One month after the transfer, many hygromycin-resistant colonies were obtained irrespective of the difference in A. tumefaciens strains used for infection. The most efficient bacterial strain was LBA4404 (pTOK233), and the addition of acetosyringone to the co-cultivation medium increased the transformation efficiency. About 90% of the hygromycin-resistant calli obtained were GUS-positive in X-gluc histochemical analysis. Introduction of foreign genes into the genome of plants regenerated from hygromycin-resistant calli was confirmed by PCR and Southern blot analysis. The transformation efficiency using the friable calli was much higher than that using leaf explants.