Abstract: The chemical compounds that induce expression of nodulation genes of Bradyrhizobium japonicum strains have been identified. The isoflavones daidzein and genistein were identified as soybean exudate components that induce nod-genes. Other isoflavones, including 7-hydroxyisoflavone, 5,7-dihydroxyisoflavone, biochanin A, formononetin and prunetin, were also found to act as inducers. In addition, several flavonoid compounds including 4',7-dihydroxyflavone, apigenin, kaempferol and coumestrol, were also found to act as inducers. Nodulation inducing compositions and a method for selectively activating the expression of a gene under the control of a soybean exudate inducible promoter in B. japonicum in response to these inducer molecules are described. In addition, soybean inoculating compositions containing the nod-gene inducers and inoculating methods employing these compositions are described.