Phytoestrogens represent a distinguished group of phytochemicals whose biological effect in mammals is clinically similar to that of exogenous estrogens. These substances may directly interfere with estrogen receptors (ER) regulated processes essential for normal physiological functions of mammalian organism. Therefore, in the presented paper we have summarized current information on the occurrence of phytoestrogens and available methods for estrogenic activity determination. We have also included data on tissue distribution and molecular characteristics of different ER subtypes, as well as, data on their interactions with phytoestrogens. Considering the important role of intracrine estrogen regulatory systems have described in separated part a ligand binding receptor method suitable for tissue level analysis. The example of experimental protocol used for determination of dietary phytoestrogens binding affinities to ER from the pituitary, uterus and thyroid gland collected from anoestrous ewes is included. The presented data fully confirm that dominant effects of phytoestrogens in mammals are caused by their direct interaction with ERs. The existence of functionally different multiple forms of ERs do not allow to create a single detection system for evaluation of phytoestrogens activity. The measurements performed using defined ER isoform result in information on its intracellular ligand activated mechanism of ER action. The analysis based on tissue ER extracts allows estimation of biologically effective concentrations of phytoestrogens. It is expected that the ongoing research on identification of ER inducible genes in vertebrate genomes may result in a more complex evaluation of estrogenic responses using proteins whose function is directly affected by phytoestrogens.