The development of polyclonal antibody-based enzyme-linked immunosorbent assays (ELISA) for the determination of individual isoflavones, i.e. daidzein, genistein and biochanin and their homologues, is presented in this work. Isoflavone conjugates with bovine serum albumin were used as immunogens, coupled at the position C 7 and C 4’ via a carboxy methyl spacer. The developed ELISAs are highly specific, I₅₀ values of the standard curves range between 0.3–1.2 ng/ml. The cross reactivities to other isoflavones are in acceptable range and the interference of non-isoflavonoid molecules is negligible. The immunoassays have been used for monitoring of changes in isoflavone levels in alimentary important plants, such as Medicago sativa, during germination; and during different vegetation stages of the Rutaceae family plants.