Persistence of the isoflavones formononetin and biochanin A in soil was investigated by HPLC analysis. Biochanin A disappeared more rapidly than formononetin in nonsterile soil. In soil planted with corn seedlings, the disappearance was dramamtic for both isoflavones. The results suggested that soil microbial populations were able to metabolize these isoflavones. The response of several microbial populations to isoflavone amendments was measured in soil samples obtained from Michigan potato fields. Results suggested that the isoflavones formononetin and biochanin A were able to stimulate the growth of soil microorganisms.