Solanum nigrum protoplasts were co-cultivated with Agrobacterium rhizogenes harboring agropine-type Ri plasmid (pRi15834). A large number of transformed calli were obtained on Murashige and Shoog's (MS) medium lacking plant growth regulators. Frequency of transformation was about 3.5×10(-3). In most of the calli, hairy roots appeared on MS medium without plant growth regulator. When the hairy roots were cut into segments and subcultured on MS medium lacking plant growth regulators, calli were readily formed. Plantlets were regenerated by transferring those calli to MS medium supplemented with 1 mg/l zeatin and 0.2 mg/l naphthaleneacetic acid. Frequency of plant regeneration was about 70%.