Despite a wide interindividual variation of cytochrome P-450 1A2 (CYP1A2) activity, genetic polymorphism of CYP1A2 has not been reported. By amplification of exons of CYP1A2 by polymerase chain reaction in eight Chinese subjects, the polymerase chain reaction products were directly sequenced. One subject showed heterozygous C2866-->G (Phe21-->Leu) polymorphism. DNA from 157 Chinese subjects (104 polychlorinated biphenyl-exposed subjects and 53 control subjects) was screened for polymorphism by single-strand conformation polymorphism method and MboII endonuclease digestion. Only 1 of 157 samples showed another heterozygous C2866-->G mutation. The subject was previously exposed to polychlorinated biphenyl and showed a value of 3.5% in the caffeine breath test. The value is not significantly higher than the mean value of polychlorinated biphenyl-exposed subjects (3.12 +/- 0.29%, mean +/- S.E.M.). The incidence of the point mutation in these Chinese subjects is less than 1%. The prevalence of the F21L mutation in other ethnic groups and its effect on the metabolic activity of CYP1A2 remain to be further evaluated.