To quantitate ductular and/or ductal bile water reabsorption and to define its role in hepatic bile formation, spontaneous and taurocholate-stimulated bile flow and composition were measured in anesthetized dogs postprandially (n = 4) and after a 24-hour (n = 4) and a 48-hour (n = 4) fasting period. Spontaneous bile flow in fed dogs (0.344 +/- 0.116 microliter/min/gm liver tissue) was significantly higher than that in 24-hour (0.179 +/- 0.046 microliter/min/gm) and 48-hour fasted animals (0.096 +/- 0.085 microliter/min/gm). One 48-hour fasted dog was virtually cholestatic (spontaneous bile flow 0.004 microliter/min/gm), and another 48-hour fasted animal had a mean bile flow rate as low as 0.036 microliter/min/gm. Calculated ductular bile water reabsorption (carbon 14-erythritol biliary clearance minus bile flow) was the same in the three groups of animals (0.166 +/- 0.056, 0.208 +/- 0.033, and 0.204 +/- 0.055 microliter/min/gm, respectively). Administration of sodium taurocholate (0.5 to 2.0 mumol/min/kg) revealed intact canalicular secretory capacity in all dogs, and no change in bile water reabsorption rate was observed during choleresis. Bile chloride and bicarbonate concentrations during spontaneous secretion were significantly lower in 48-hour fasted dogs when compared with fed animals. In the two 48-hour fasted dogs with a very low rate of spontaneous bile flow, chloride and bicarbonate concentrations in hepatic bile were as low as those seen in gallbladder bile (5 to 10 mEq/L) and increased during taurocholate choleresis.(ABSTRACT TRUNCATED AT 250 WORDS)