The influence of dehydrocholate on bromsulphtalein relative-storage capacity, bilary transport maximum (Tm), and fractional transfer rates between plasma, liver and bile have been studied in unanaesthetized dogs. In six dogs, storage capacity, Tm, and fractional transfer rates from plasma to liver, liver to bile, and liver to plasma were measured during 0-15 M NaCL infusion and the measurements were repeated under a dehydrocholate infusion of 95 mumol. min-1, ie, an infusion rate approaching the known biliary Tm of bile salts. It was found that: (a) storage capacity and fractional transfer rates from plasma to liver significantly lower during dehydrocholate infusions (respectively 18-0 plus or minus SD 9-0 mg-mg-1. 100 ml-1 and 0-120 plus or minus SD 0-035 min-1) than during NaCL infusions (respectively 47-0 plus or minus 21-0 mg. mg-1. 100 ml-1 and 0-280 plus or minus SD 0-055 min-1; P smaller than 0-001); (b) Tm and fractional transfer rates from liver to bile were also significantly lower during dehydrocholate infusion (respectively 3-2 plus or minus SD 1-1 mg. min-1 and 0-013 plus or minus SD 0-004 min-1) than during NaCl infusion (4-8 plus or minus SD 1-1 mg. min-1 and 0-033 plus or minus SD 0-017 min-1; P smaller than 0-02); (c) in three additional experiments, taurocholate had similar effects on storage capacity and Tm. These findings suggest that competition occurred between bile salts and bromsulphthalein for hepaticuptake and storage. They support the hypothesis that the decreased disappearance rate and relative storage capacity of bromsulphtalein observed during biliary obstruction may be due to competition between bile salts and bromsulphthalein for hepatic uptake and storage.