Summary: An enzyme was detected in normal urine that was identical to plasma renin in all respects tested and was totally inhibited by antibody to human renin. A method is described for its quantitative determination involving incubation with a standard substrate in an angiotensinase‐free medium and measurement of velocity of angiotensin formation by bioassay. The recovery of renin through the method is complete. Errors due to the action of pepsin forming pepsitensin from renin substrate were avoided by incubating at pH 7·5. The concentration of renin in normal random male urine averaged 0·07 that of plasma.