Bilary re-excretion of sulfobromophthalein sodium (BSP) (1.2 mumol/rat) after retrograde intrabilary injection is markedly inhibited by dehydrocholate sodium (Decholin) given intravenously as a constant infusion (3.1 mumol/min/kg body weight) or as a bolus injection (24.8 mumol/rat) to rats. Most interestingly Decholin demonstrates the same inhibitory effects on the biliary re-excretion of BSP when it is administered by retrograde intrabiliary injection (24.8 mumol/rat) together with the dye. In contrast to the inhibition of biliary re-excretion of BSP its biliary reabsorption from the biliary tract seems to be rather increased: about 80-85% of 1.2 mumol BSP are reabsorbed in all sets of experiments with Decholin in comparison to about 65% to the control group. Combined with histological data it is suggested that reabosorption of BSP after retrograde intrabiliary injection occurs at the ductular site whereas re-excretion takes place at the cannalicular membrane of the hepatocyte.