BACKGROUND: Chronic obstructive pulmonary disease (COPD) is characterized by the presence of a low-grade systemic inflammation that is implicated in the pathogenesis of numerous extrapulmonary manifestations, such as hypogonadism. Endothelin-1 (ET-1) is a molecule that demonstrates pro-inflammatory properties and can augment the airway and systemic inflammation. Single nucleotide polymorphisms (SNPs) of the ET-1 gene that increase ET-1 serum levels are an important area of investigation. We examined the alterations in inflammatory markers [C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)] and in the levels of testosterone, free testosterone, follicle stimulating hormone (FSH) and luteinizing hormone (LH) in a group of male COPD smokers when compared to their age-matched controls and how these alterations relate to the presence of a functional ET-1 SNP, the adenine insertion SNP +138 insA/delA. MATERIALS AND METHODS: In this case control study, 80 male control smokers and 82 male COPD smokers were recruited for comparison. Among the male COPD smokers, 37 were carriers of the +138 insA/delA SNP. Two COPD subgroups according to genotype were formed: (1) A group of 45 males homozygous for the wild type allele (3A/3A) and (2) a group of 37 males heterozygous for the mutant allele (3A/4A). RESULTS: Levels of testosterone and free testosterone were lower in the COPD group and even lower in the 3A/4A COPD group. CRP and ESR levels were higher in both COPD groups, but their elevation was statistically significant only for the 3A/4A COPD group. Testosterone and free testosterone levels correlated positively with PaO2 for both COPD groups. An inverse correlation between testosterone and CRP was demonstrated for the 3A/4A COPD subgroup. CONCLUSIONS: Levels of testosterone correlated to FEV1, hypoxemia and weakly to CRP. The synchronous presence of the +138 insA/delA SNP resulted in even greater sex hormone level decline probably due to the presence of a more intense systemic inflammation.