[en] A method for measurement of plasma renin activity is described in which angiotensin I, generated during a 3 or 18 hour incubation period is quantitated by radioimmunoassay. The incubation step is carried out in undiluted plasma at the pH optimum (pH 5.7) with complete angiotensinase and converting enzyme inhibition by EDTA and DFP. Blank subtraction is eliminated by the generation of large amounts of angiotensin during incubation, which also increases the accuracy of the measurements. Recommendations for modification of commercially available kits include changes in the incubation step for generation of angiotensin I. A trouble-shooting section is included in which changes in the radioimmunoassay step are pointed out, which provide clues to possible errors and to sources of variability. (U.S.)