We have quantified genotype frequency of the cytochrome P450(P450) 1A1, which is primarily responsible for the metabolic activation of carcinogenic polycyclic aromatic hydrocarbones, in Korean population by PCR and RFLP at two sites associated with lung cancer; MspI RFLP in the 3' flanking region of the gene and NcoI RFLP in exon 7(a point mutation of isoleucine to valine substitution) near the catalytic region of the enzyme. The genotype frequencies of homozygous wild type (MspI site-absent), heterozygous mutant type (MspI site-present), and homozygous mutant type in MspI RFLP were 0.45, 0.42, and 0.13, respectively. The genotype frequencies of homozygous wild type (IIe/IIe) and heterozygous mutant type (IIe/Val) in NcoI RFLP were 0.54 and 0.46, respectively. The homozygous mutant type (Val/Val) in NcoI RFLP was not observed in Korean population.