Neuroendocrine activity in normal subjects was compared to patients with chronic renal failure on maintenance hemodialysis (CRF-HD) and to cyclosporine- treated renal transplantation (RT) recipients in an effort to further define the mechanisms underlying their associated fluid, electrolyte, and hemodynamic abnormalities. To evaluate neuroendocrine function in CRF and RT patients, plasma levels of angiotensin II (A-II), vasopressin (AVP), atrial natriuretic peptide (ANP), neuropeptide Y, neuropeptide Y (NPY), epinephrine (E), and norepinephrine (NE) were measured before and after HD and RT. Plasma concentrations of A-II, AVP, ANP, and NPY were significantly elevated in patients with CRF. HD did not produce a significant change in plasma concentrations of AVP, ANP, NPY, E, or NE. NE plasma levels, but not E levels, increased pre- and post-HD. A-II plasma levels were elevated basally in CRF patients and significantly increased following HD. Following RT, plasma levels of A-II, AVP, NPY, and creatinine decreased significantly over the first week, but AVP and NPY did not normalize. Plasma levels of ANP were elevated during the first month, then decreased to normal levels in RT patients. NE levels, but not E levels, were elevated both pre- and post-RT. Despite antihypertensive treatment, the group mean arterial pressure increased post-RT from 100±4.4 to 116± 3.7 mmHg by POD 6.