In this study of 221 lung cancer patients and 212 controls, no association between aMspI polymorphism in theCYP1A1gene and an increased risk of lung cancer was found. Histological type, smoking habits and family history were also examined. No associations between theMspI restriction fragment length polymorphism in theCYP1A1gene and any of these parameters were found. These results are in contrast to a previous report by a Japanese group (Kawajiriet al.,1990) who found an association between the less common allele and an increased susceptibility to lung cancer in their population. The frequency of the less commonMspI 1.9 kb fragment allele (C2) appears to be three times greater in the Japanese population than in the Norwegian population and a Caucasian population of North America. It is possible that in the Asian population thisMspI polymorphism is in linkage disequilibrium with another mutation important forCYP1A1gene expression, whereas in the Caucasian population these mutations are in equilibrium