The principle of operation of the kit is based on the fact that the tested sample with endocrine activity (containing compounds capable of binding to the human estrogen receptor α, hERα) releases the fluorescently labeled ligand (FluormoneTM ES2) from the receptor-ligand complex, which results in a reduction of the polarization value fluorescence. The maximum value of fluorescence polarization is shown by the receptor-ligand complex, while the minimum mixture containing additionally 1 µM 17β-estradiol (the sex hormone with the highest biological activity).The endocrine potential of the tested samples was compared with the activity of estradiol by determining the endocrine equivalent concentration (EEQ).