Membrane prolactin receptor exhibit differences in both interspecies and intra. The occurrence of different variants of the receptor (isoforms) in the organs and tissues of the same individual can adjust the signal transmitted by the hormone. The article presents an overview of the various isoforms of the receptor expression in human and various animal species, and the latest data on the subsequent intracellular processes which occur upon binding of a ligand to a receptor activation step of specific genes.