Renin is produced from an inactive precursor, prorenin, through endoproteolytic cleavage at paired basic amino-acid residues. Using (35S)methionine-labeled prorenin, that was synthesized with Xenopus oocyte expression system, as a substrate, we have determined the tissue distribution and the nature of prorenin-converting activity in mouse. The highest activity was found in the submandibular gland of male ICR mouse. The activity of the enzyme seemed to be parallel to that of renin. This enzyme activity, with an optimal pH 8.0-8.5, was inhibited by leupeptin, antipain and benzamidine.