A crossover experimental design was used to examine the effects of saline (SAL) vs. taurocholate (TC) infusion on hepatic excretory function in isolated perfused livers from pregnant (19-21 days gestation) and nonpregnant female rats. Bile flow, bile acid concentration, bile acid secretory rate, dibromosulfophthalein (DBSP) concentration in bile, and DBSP secretory rates were determined in livers infused continuously with DBSP and initially with SAL (1 ml/hr, 45 min), followed by TC (60 mumol/hr, 1 ml/hr; 75 min) or initially with TC (45 min) followed by SAL (75 min). The order of infusion (SAL-TC vs. TC-SAL) had no significant effect. TC infusion significantly increased all measures in livers from both nonpregnant and pregnant rats. Two-way analysis of variance followed by the Tukey-Kramer test showed that bile flow (microliter/min/g liver) and DBSP concentration in bile (mumol/ml) were significantly decreased during SAL infusions in pregnancy. These two measures plus bile acid and DBSP secretory rates (nmol/min/g liver) were also significantly decreased during TC infusion in pregnancy. Pregnancy had no effect on bile acid concentration in the presence of SAL or TC infusions. When bile flow, bile acid, and DBSP secretory rates were calculated per whole liver, only the DBSP secretory rate was significantly decreased in pregnancy. These data indicate that bile flow and bile acid secretion do not increase in proportion to the increase in liver weight in pregnancy so that these measures are decreased when expressed per g liver. Pregnancy appears to have a real inhibitory effect on DBSP since its secretion is depressed when activity is expressed per g liver or per whole organ.