We have isolated four overlapping human genomic clones associated with the polynuclear aromatic hydrocarbon-induced form of cytochrome P-450. The form of P-450 most closely associated with polynuclear aromatic hydrocarbons induction has been defined as P1-450. These four overlapping genomic clones span a total of 31.0 X 10(3) base pairs in length with the coding sequence lying in the center of these clones. Translation in vitro of 3-methylcholanthrene-induced mRNA, selected with the human P1-450 genomic clone, detect a protein with Mr 52000, which is immunoprecipitable by the anti-(mouse P1-450) antibody. The isolated human P1-450 genomic clone hybridizes to 3-methylcholanthrene-induced mRNA from monkey liver, benzanthracene and 3-methylcholanthrene-treated human mammary tumor cells (MCF-7), but not to isosafrole-treated human cells. Upon treatment with polynuclear aromatic hydrocarbons there is a positive correlation between induced arylhydrocarbon hydroxylase (flavoprotein-linked monoxygenase) activity and the amount of mRNA that hybridizes to the isolated human genomic clone for P1-450. The size of mRNA, induced from human cells and monkey liver by polynuclear aromatic hydrocarbons, is around 3.3 X 10(3) base pairs, which is the same as the larger of two mRNA induced by polynuclear aromatic hydrocarbons in the inbred strain of mouse (C57BL/6N). Our data also showed that the isolated DNA clone can detect a mRNA size of 3.3 X 10(3) base pairs from phytohemagglutinin-activated, benzanthracene-treated human lymphocytes. Densitometer scanning indicated the presence of a 3.6-fold variation (highest-lowest) in the levels of lymphocyte P1-450 mRNA contents among six individuals studied.