This paper presents our experience in measurement of plasma angiotensin II concentration according to the method described by Düsterdieck, G. and McElwee, G. (1971) Eur. J. Clin. Invest. 2, 32-38. Certain technical modifications of the procedure have been worked out. For each individual plasma sample, the recovery across extraction and elution steps is determined by addition of radio-iodinated angiotensin II. A time-saving recycling elution procedure is described. Evidence for the clinical applicability of the modified method is presented.