A comparative study of human CYP1A1 genotypes and enzymatic activity was performed in a racially diverse population in order to determine frequencies of CYP1A1 genetic polymorphisms and the relationship between CYP1A1 genotype and function. Restriction fragment length polymorphism analyses revealed significantly higher frequencies of a variant Msp1 polymorphism in Asians versus European-Americans, while African-American CYP1A1 genotypic frequencies more closely approximated those of Asians. Comparison of CYP1A1 genotypes at the Msp1 locus to a polymorphic site in exon 7 of the gene revealed a higher frequency of variant genotypes at the Msp1 site. Measurement of lymphocyte CYP1A1 enzyme activity by the ethoxyresorufin O-deethylase assay revealed significantly elevated levels of inducible enzyme activity among variant exon 7 genotypes when compared to wild-type genotypic individuals. These results demonstrate racially distinct patterns of CYP1A1 genotypes, and suggest a functional link between genotype and catalytic activity of the cytochrome P-450 protein responsible for the metabolism of many carcinogenic polycyclic aromatic hydrocarbons.