Standard Gamborg's (B5), Murashige and Skoog's (MS) basal media, half strength medium of these media and N6 medium were used in the experiments. To determine the effects of different NH4+ to NO3- ratios on hairy root growth, conventional MS medium was modified in such a way that total NO3- and NH4+ ions were supplied from KNO3 and (NH4)2SO4 salts, respectively.