Chronic cervical spinal cord injury is characterized by defects in sodium and water homeostasis and defects of adaptive hormonal responses. The plasma osmolality is maintained in a relatively narrow range, the lower limit of which is determined by osmotic threshold for vasopressin release and the upper limit by the third threshold. Antidiuretic hormone as an important mediator of fluid and electrolyte balance was well investigated in able bodied children comparing children with normal voiding pattern and children with enuresis. The normal subjects were found to have higher plasma ADH at night, not detected in the group with enuresis. The findings were similar in elderly patients with increased diuresis at night, suggesting an important role of ADH in nocturnal decrease of urine output. Investigators studied the effect of rapid tilt on plasma ADH in tetraplegic compared with normal subjects, but there are no data available in the literature regarding ADH and its effects on water and electrolyte balance in healthy tetraplegic subjects with a normal lifestyle. We decided to undertake a pilot study to attempt to establish baseline ADH levels in this subject group, to better understand and manage tetraplegic patients with water and electrolyte dysregulation. Our preliminary data suggest that these individuals lack the normal diurnal variation of ADH, a phenomenon similar to that demonstrated in enuretic children and elderly, and furthermore appear to have generally depressed ADH levels.