Xenobiotics are chemical compounds which are foreign to the body. The term detoxification is now being replaced by the more appropriate biotransformation. Xenobiotics are metabolize into two phases. Phase I reactions involve oxidation, reduction and hydrolysis. The major reaction of phase I is hydroxylation catalyzed by monooxygenases also called cytochrome P450 or mixed function oxidases. In phase II compounds produced in phase I are converted to polar metabolites by conjugation with various conjugating agents, e.g. UDP-glucuronate, Glutathione, Glycine, etc.