1. The effect of chronic bile-duct ligation on systemic and renal haemodynamics and on the capacity to dilute the urine was studied in conscious rats. Sham-operated rats served as controls.
2. In the rats with bile-duct ligation, the maximal urinary diluting capacity was impaired, despite an expanded plasma volume, a normal mean arterial pressure and cardiac output, and normal intrarenal determinants of water excretion including distal delivery of fluid and function of the diluting segment.
3. In contrast, maximal urinary dilution capacity was intact in rats with congenital central diabetes insipidus and chronic bile-duct ligation.
4. It is concluded that the defect in urinary dilution in rats with chronic bile-duct ligation is dependent on antidiuretic hormone.