When considering only those COPD patients with FEV1/VC < 0.7 (n = 263), the NOS3-VNTR SNP genotype association remained statistically significant in a t-test analysis (4bb, mean (SD) 43.5 mmHg (11.8), n = 186 vs 4ab/4aa, mean (SD) 47.1 mmHg (14.6) n = 77, P = 0.034). This evidence concerns the gene NOS3 and chronic obstructive pulmonary disease.