1. Patients with cadaveric renal transplants and plasma creatinine less than 177 micronmol/l who had their own kidneys removed were studied. 2. The renin-angiotensin system appeared to behave in a normal fashion in response to alterations in sodium intake and posture. 3. The renin-angiotensin system had no major role in the establishment or maintenance of hypertension. 4. Mean arterial pressure was directly related to expansion of the extracellular fluid volume.