This study investigated the effect of Brefeldin A (BFA) on the transcytotic vesicular pathway labeled with horseradish peroxidase (HRP) in both isolated rat hepatocyte couplets (IRHC) and the isolated perfused rat liver (IPRL). To evaluate the role of the transcytotic vesicular pathway on bile secretion, the effect of BFA on bile secretion in the IPRL was then investigated. In the basolateral area of IRHC, BFA showed no effect on the density and percentage of area of HRP-labeled vesicles. However, HRP-labeled vesicles tended to accumulate in the juxtanuclear area of BFA-treated hepatocytes (P < .001 vs. controls). In the pericanalicular area, on the other hand, HRP-labeled vesicles were depleted compared with controls (P < .001). In keeping with these findings, although the early peak remained unchanged, BFA inhibited as much as 50% of the late peak of HRP excretion in bile, after a pulse load of HRP in the IPRL. Bile flow and the biliary secretion of bile salts (BS) and phospholipids were not modified by BFA in isolated livers perfused without BS in the perfusate or with 1 mumol/min taurocholate (TCA). In BFA-treated livers, peak bile flow and BS output decreased by 20% (P < .05 vs. controls) only when a 5 mumol TCA bolus was administered. In conclusion, this study demonstrates that BFA inhibits the transcytotic vesicular pathway in the liver. However, BFA has no significant effect on bile secretion either in basal conditions or during perfusion with physiological amounts of BS. BFA slightly decreases bile flow and BS output only after an overload of BS, providing evidence against the physiological relevance of the transcytotic vesicular pathway in the process of bile formation.