CYP1A1 is considered to be involved mainly in oxidative metabolism of exogenous chemicals and drugs. Synthesis of this hemoprotein is induced in livers, lungs, and other tissues of experimental animals by the administration of these chemicals. Regulatory mechanisms of the induction process of the protein have been investigated by the DNA transfer method using the isolated genomic DNA. At least two kinds of cis-acting regulatory DNA sequences are localized 5' upstream of the gene. One is distributed five times in a relatively wide range from -0.5 to -3.5 kb and functions as an inducible enhancer-designated xenobiotic responsive element or XRE. The other is localized just upstream of the TATA sequence and acts as a regulatory element for the constitutive expression. The two DNA elements are required for a high level of the inducible expression. Their cognate DNA binding factors are recognized in the nuclear extracts of Hepa-1 cells and rat liver cells which show the inducible expression of CYP1A1 in response to the inducer. This paper discusses the regulatory mechanisms of CYP1A1 gene expression by summarizing the present state of knowledge about properties of the DNA regulatory elements and their cognate DNA-binding factors.