The liver is the primary organ of metabolism and disposition for most compounds. The portal vein carries blood, and parent compounds, from the gastrointestinal tract to the liver. Compounds are taken up into the hepatocytes through passive diffusion and/or active uptake by transport proteins present on the basolateral membrane of the hepatocytes. Once inside the hepatocyte, compounds may undergo metabolism, and the parent and/or generated metabolites may be excreted across the canalicular membrane into the bile or across the basolateral membrane into systemic circulation. Our investigations of metabolism help our clients understand the hepatobiliary disposition, toxicological properties, and DDI potential of parent compounds and metabolites.