The goal of the proposed research is to examine the development of hepatic excretory detoxification mechanisms. These experiments will yield information that might help to explain differences in toxicity of some drugs and other foreign chemicals between newborn and adult animals. Results obtained by the study may also help to determine the dosage of drugs that should be given to newborns, as well as helping in the choice of drugs to be used in newborns. By examining the excretion of drugs and other foreign chemicals by the liver of very young to adult animals, a deeper insight into the basic mechanisms of detoxification of drugs by biliary excretion will be gained, an area in which development has lagged relative to detoxification by metabolism and renal excretion.