Transformed hairy roots of Psoralea corylifolia were established by infection with Agrobacterium rhizogenes LBA 9402. The aim of this work was to elucidate the effects of media constituents on production of the phytoestrogenic isoflavones daidzein and genistein. A. rhizogenes strain LBA 9402 harboring Ri plasmid was used to transform stem segments of in vitro seedlings. The resultant hairy roots were confirmed by polymerase chain reaction (PCR) and exhibited Ri T-DNA. Transformed hairy root clones were cultured in Murashige and Skoog's (MS) medium altered with different concentrations of NH₄+ and NO₃- and their growth and production of isoflavones were assessed. Biomass and productivity increased when MS medium was supplemented with NH₄+ and NO₃- at a ratio of 20:10. Increased yield of daidzein was obtained when sucrose level in the culture medium increased, whereas decreased level of sucrose favored genistein production. The hairy roots produced the highest levels of daidzein (2.06% dry wt.) and genistein (0.37% dry wt.) in the presence of low concentrations of PO₄3^-. Hairy roots secreted trace amounts of daidzein and genistein into the culture medium. The present results demonstrated that the productivity of daidzein was 2.2-fold more than that of untransformed roots.