A native human prorenin and a mutant of its processing site (Arg-43 to Gln) were expressed in mouse pituitary AtT-20 cells which process prorenin to renin and have both regulated and constitutive secretory pathways. The native prorenin was processed to renin and secreted in a regulated manner. Although the mutant precursor was not processed, it was also secreted in a regulated manner. These results suggest that prorenin is sorted into the regulated pathway, stored in secretory granules and released by stimulus whether it is processed to renin or not.