AnAgrobacterium-mediated transformation system has been developed for introducing foreign genes into the three most important potato cultivars in New Zealand (‘Ilam Hardy’, ‘CRD Iwa’, ‘CRD Rua’). Leaf segments of in vitro plants were co-cultivated with a disarmed strain ofAgrobacterium twnefaciens(LBA4404) harbouring the binary vector pCGN200. This vector contains two chimeric neomycin phosphotransferase genes (OCS-NPT II-OCS and 35S-NPT II-TML) that confer kanamycin resistance to plant cells. Potato cell colonies were selected with resistance to 250 mg/litre kanamycin and regenerated into complete plants. Proof that these plants were transformed involved both biochemical and molecular evidence. Enzymatic expression of neomycin phosphotransferase II was detected in leaf extracts using a dot blot assay. Southern analysis confirmed integration of the foreign DNA into the potato chromosomal DNA. The cultivar ‘Iwa’ was especially amenable to bothAgrobacterium-mediated transformation and the regeneration of transgenic plants.