Objective
To delineate the role of antidiuretic hormone (ADH) in relation to nocturnal polyuria, and to identify the factors influencing on the diurnal antidiuretic hormone level.

Method
The ADH was measured by radioimmuoassay at daytime (2:00 PM) and at nighttime (2:00 AM) with nocturnal polyuria group (11) and without nocturnal polyuria group (8). Urine volume, serum osmolarity, urine osmolarity, and blood pressure were also measured at the same time.

Results
1) The ADH at 2:00 AM did not increase in nocturnal polyuria group, although it increased in no-symptom group. 2) There was a statistically significant correlation between wheelchair ambulation time and daytime ADH level. 3) The difference of ADH level between daytime and nighttime showed decrease in orthostatic hypotension group.

Conclusion
There was relationship between nocturnal polyuria and diurnal variation of ADH level. The ADH concentration seems to be influenced by the postural factors and sympathetic factors.