Measures to control smoking are important in the field of preventive medicine. In order to clarify differences in susceptibility in individuals to lung cancer of genotypes of CYP1A1, which are considered to be related to lung carcinogenesis were evaluated in 391 healthy males to study relationship to smoking status and hematological findings. No correlation was observed between genotypes of CYP1A1 and smoking status. White blood cell counts in smokers with a Val allele were significantly higher than in those without a Val allele. Multiple regression analysis showed that the genotype of CYP1A1 and daily cigarette consumption had significant relationship with white blood cell count in smokers. However, red blood cell count, hemoglobin, hematocrit, MCV, MCH, or MCHC were not significantly associated with genotype of CYP1A1. There have been no previous reports on the relationship between the genotype of CYP1A1 and hematological findings. In consideration of the epidemiologic findings that many individuals with increased white blood cell counts have cancer or cardiac diseases, and reports that the increase in the white blood count was associated with poor respiratory function, white blood cell count may be candidate to for being a risk marker and thus contribute to prevention of these diseases.