Transformed root cultures of Withania somnifera Dunal (Solanaceae) were obtained by infecting shoots cultured in vitro with Agrobacterium rhizogenes LBA 9402. They grew axenically in the absence of exogenous plant growth regulators in Murashige and Skoog's medium containing 3% (w/v) sucrose. The root cultures synthesized several withanolides of which withanolide D was isolated and identified. Transformed root (clone HR1) showed a growth index of 20.07 and a withanolide D yield of 0.30 mg g-1 DW. The productivity of withanolide D in transformed roots (0.181 mg 1-1 1) was higher than in untransformed root cultures (0.026 mg 1-1 d-1).