BACKGROUND: Oxidative damage is a major contributing factor to carcinogenesis and obstructive disorders in lungs. Current evidence suggests that the inflammatory processes yield to oxidative mechanisms, which underlie COPD, lung cancer, and obstructive sleep apnea syndrome (OSAS). This study aimed to evaluate the oxidative damage in these diseases by evaluating the oxidative and antioxidant biomarkers. METHODS: Malondialdehyde, 8-oxo-7,8-dihydro-2'-deoxyguanosine, and coenzyme Q10 levels were evaluated in the blood samples of subjects with COPD, lung cancer, and OSAS by high-pressure liquid chromatography. RESULTS: A total of 111 participants (35 females, 76 males) with OSAS (n = 29), COPD (n = 26), and lung cancer (n = 28) and healthy controls (n = 28) were included in the study. The malondialdehyde and coenzyme Q10 levels were significantly higher in all 3 diseases when compared with controls (P < .01), whereas 8-oxo-7,8-dihydro-2'-deoxyguanosine levels were only significantly higher than in healthy controls in subjects with lung cancer (P = .005). The highest levels of malondialdehyde and coenzyme Q10 were determined in subjects with OSAS and lung cancer, respectively. The highest 8-oxo-7,8-dihydro-2'-deoxyguanosine levels were also observed in subjects with lung cancer, but the differences of this biomarker with other diagnoses were not statistically significant (P = .56). CONCLUSION: Oxidative damage was observed in all 3 diagnoses, and, as a response to oxidative stress, antioxidant mechanisms were also active in these diseases. Malondialdehyde and 8-oxo-7,8-dihydro-2'-deoxyguanosine were found to be efficiently usable in the evaluation of oxidative damage in chronic respiratory diseases.