Daidzein is an isoflavone found widely in legume and other plant species. It is common in many microbial fermentations containing soy or other related plant-based extracts. Like genistein, daidzein has been widely reported as an antibacterial and anticancer active. Genistein also has antioxidant and bond protective activity, and inhibits calmodulin, reverse transcriptase and tyrosine kinase. Daidzein is an essential dereplication and bioassay standard in microbial natural product discovery. More recently, daidzein as a major component of soy products, has been established as a nutraceutical.