Sulfobromophthalein (BSP) is stored in the liver during its passage from plasma to bile. The soluble hepatic anion-binding protein, ligandin, may be responsible for BSP storage since BSP binds to this protein. Studies were undertaken in rats and dogs to determine whether the amount of ligandin in the liver is a major determinant of storage. Ligandin content in dog liver was found to be 0.252 mg BSP bound/kg body wt which was about one-half that in rat liver (0.504 mg BSP bound/kg body wt). Relative to plasma, BSP accumulation in liver tissue (or storage of BSP) following single bolus injection of BSP was about 5 times greater in rats than in dogs. Lack of correlation between BSP accumulation and ligandin content suggests that intracellular storage of this anion is not solely determined by its binding to ligandin. Differences in the carrier-mediated transport processes on either/or both sinusoidal and canalicular sides of the hepatocyte may be responsible for this affect.