Native human renin, produced from the culture of human chorionic trophoblasts, has been purified to homogeneity on a milligram scale using a five-step purification scheme. The chorion cells secrete 50-200 milliGoldblatt Units of trypsin-activatable prorenin per ml into the medium. The pro-enzyme is partially purified by ammonium sulfate fractionation and chromatographies on QAE-Sephadex and cibracon blue-agarose. Following conversion of prorenin to the active enzyme by porcine trypsin, the renin is purified to homogeneity by affinity chromatography and gel filtration. Chorionic prorenin has a molecular weight of 43,000; the active enzyme 40,000. Both proteins exist as a single polypeptide chain as determined by SDS-polyacrylamide gel electrophoresis under reducing conditions. The average specific activity of six different preparations was found to be 1072 Goldblatt Units/mg. The amino acid composition and N-terminal sequence of the active enzyme has been determined and is identical to the human kidney enzyme. Microheterogeneity of chorionic renin was demonstrated by isoelectrofocusing analysis. The physical characterization of chorionic renin is compared with that reported for the human kidney enzyme.