Renalase, a recently discovered protein participating in the catecholamine metabolism and belonging to oxidoreductases, possess also antihypertensive and cardioprotective properties, confirmed in several studies on animal models. In human, rat and mouse renalase is thought to be produced mainly by kidney, but increasing number of reports indicates that large quantities of this enzyme, depending on species, are produced by other organs, primarily heart and gonads. However, there are still many uncertainties regarding the mechanism of in vivo action of renalase. The discrepancies in the results of measurement of its concentration in patients with chronic kidney disease exist. Moreover, the site of production and the potential biological function of the renalase isoforms, except isoform 1, are still not determined.