We present the genotype distribution of the CYP1A1 gene in a sample of over 300 subjects of various ethnic origins. Genotypes are presented as composites of eight possible alleles, taking into account the three major polymorphisms, including a recently described African-American-specific MspI RFLP. A new nomenclature system is presented for clarifying the various haplotypes. Interesting interracial differences in allelic frequencies and admixture rates were observed for the three polymorphisms. Because of the importance of the CYP1A1 gene (which encodes the aromatic hydrocarbon hydroxylase) as a biomarker of genetic susceptibility to environmental carcinogens such as polycyclic aromatic hydrocarbons, these data may provide a useful reference for future studies of relationships between CYP1A1 genotype and disease susceptibility.