['To explore the effects of continuous positive airway pressure (CPAP) treatment on the serum levels of associated inflammatory factors in patients with overlap syndrome (OS).', 'Seventy-four patients with obstructive sleep apnea syndrome (OSAS) or chronic obstructive pulmonary disease (COPD) or overlap syndrome (OS) were recruited from Department of Respirology and Affiliated Sleep Center of our hospital from March 2012 to September 2013. They were divided into OSAS (n = 25), COPD (n = 26) and OS (n = 23) groups according to the results of polysomnography (PSG) and spirometry. By enzyme linked immunosorbent assay (ELISA), the serum levels of C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-α) and asymmetric dimethylarginine (ADMA) were measured and compared before and at Day 30 post-CPAP in OSAS and OS groups.', 'At pre-CPAP, there was no statistical difference in serum levels of CRP ((7.2 ± 6.6),(8.4 ± 6.8),(8.5 ± 7.9) mg/L) and TNF-α ((33 ± 13),(52 ± 34),(41 ± 33) ng/L) among OSAS, COPD and OS groups (all P > 0.05).However, serum ADMA level in OSAS group were significantly lower than those in COPD group ((0.50 ± 0.08) vs (0.71 ± 0.31) µmol/L, P = 0.002). Compared with before and at Day 30 post-CPAP, although no significant difference existed in serum levels of ADMA (all P > 0.05), at Day 30 post-CPAP there were significantly lower serum levels of CRP ((4.5 ± 4.2) and (5.5 ± 4.1) mg/L) and TNF-α levels ((31 ± 9) and (35 ± 24) ng/L) than those pre-CPAP in OSAS and OS groups respectively (all P < 0.05).No significant difference existed between OSAS and OS groups (all P > 0.05).'] Do [ Effects of continuous positive airway pressure treatment of inflammatory factors in patients with overlap syndrome ]?