Chinese hamster ovary (CHO) cells, transfected with a vector containing cDNA coding for preprorenin, have been shown to secrete authentic prorenin into the culture supernatant. Purification of the expressed prorenin and purification of active renin, generated by solid-phase trypsin treatment of the conditioned media, have been achieved by conventional chromatographic methods. Scale-up of the initial steps of these procedures is described, including the use of radial-flow columns and automation with fast protein liquid chromatography valves and pumps. This semi-preparative scheme has allowed hundreds of milligrams of both proteins to be isolated.