Bile flow may be considerably increased in human cirrhosis. The mechanism of this increase has not been established. Two mechanisms have been proposed: a) increased canalicular filtration because of sinusoidal hypertension, or b) secretion by proliferated bile ductules. To distinguish between these two possibilities, we examined the determinants of bile secretion in rats with secondary biliary cirrhosis after bile duct obstruction. Sham-operated animals served as controls. Four weeks after bile duct ligation, all animals had cirrhosis. Bile flow was significantly higher and bile salt secretion significantly lower in cirrhotic animals than in controls. Biliary bicarbonate concentration was significantly higher in cirrhotic animals than in controls. Bile-to-plasma concentration ratio of erythritol was significantly lower in cirrhotic animals than in controls, suggesting a dilution of erythritol by a secretion distal to bile canaliculi. Bile-to-plasma ratio of sucrose was not significantly different in cirrhotics and controls, suggesting that paracellular permeability was not modified. Secretin, at the dose of 3 clinical units/100 g, induced an increase of approximately 75 percent in bile flow, and 70 percent in biliary bicarbonate concentration in cirrhotics. In conclusion, bile flow was increased in biliary cirrhosis in rats. The dilution of erythritol, the increase in biliary bicarbonate concentration and the increased response to secretin strongly suggest that increased choleresis was due, at least in part, to secretion by bile ductules or ducts. These results confirm that secondary biliary cirrhosis is a good experimental model for the study of alterations of bile secretion in cirrhosis.