Changes in cellular isoflavone (daidzein and genistein) contents were monitored in root cultures of Albizzia kalkora (Roxb.) Prain after feeding different ratios of NH4+/NO3- and treatment with a biotic elicitor (three strains of Rhizobium sp.). The NH4+/NO3- ratio appears to be positively correlated with daidzein content in the roots and shows a negative correlation with genistein. Among the three different strains of Rhizobium used, the strain ATCC 15834 caused a 35% increase in daidzein production by infection. In the case of genistein, maximum production (94%) was obtained when cultures were treated on Day 6 by the strains ATCC 15834 and KCTC 1541. The biosynthetic pathway of the two isoflavones apparently reacts differently to the same culture conditions and the same strains of Rhizobium. Therefore, the present data suggest that the production of daidzein and genistein could be modulated by changing the NH4+/NO3- ratio and the application of Rhizobium.