The objectives of this study were to examine the possible involvement of endothelial nitric oxide synthase (ecNOS) and angiotensin-converting enzyme (ACE) genes in the genetic basis of lung cancer. Two hundred eighteen patients with lung cancer and 121 healthy subjects were included in this study. The ecNOS and ACE genotypes were determined in all subjects by polymerase chain reaction. The distribution of genotypes of ecNOS gene was significantly different in the lung cancer group than in the control population. ACE genotype distribution was not significantly different in the lung cancer group compared with the control group. These results suggest that polymorphisms of the ecNOS gene, but not the ACE gene, may be associated with the development of lung cancer.