Cytochrome P450 enzymes, a superfamilyof b-type heme-containing proteins found in organisms from alldomains of life, are major catalysts in the oxidative transformationof a diversity of endogenous and exogenous compounds. CYP enzymes play an important role in the metabolic activation of environmental procarcinogens or chemical carcinogenesis, these enzymes are monooxygenases which catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids and other lipids. The enzyme localizes to the endoplasmic reticulum and metabolizes procarcinogens such as polycyclic aromatic hydrocarbons and 17beta-estradiol. Mutations in this gene have been associated with primary congenital glaucoma; therefore it is thought that the enzyme also metabolizes a signaling molecule involved in eye development, possibly a steroid. CYP26A1 is a 497aa enzyme in mouse, rat and human (chr 10q23) and a distinct composite retinoic acid response element underlies the complex regulation of retinoic acid metabolism. This endoplasmic reticulum protein acts on retinoids, including all-trans-retinoic acid (RA), with both 4-hydroxylation and 18-hydroxylation activities. This enzyme regulates the cellular level of retinoic acid which is involved in the regulation of gene expression in both embryonic and adult tissues. Highest levels of expression are noticed in adult liver, heart, pituitary gland, adrenal gland, placenta and regions of the brain.