United airway disease (UAD) concept proposed that asthma and rhinitis are both different clinical manifestation of a single inflammatory process. The aim of this study is to assess in upper and lower airways the level of inflammation and oxidative stress and to investigate the relationship between biomarkers in persistent allergic rhinitis (PER) and in concomitant asthma with PER. By a crosssectional study we measured oral and nasal (FENO) and oral and nasal EBC 8-isoprostane, LTB4 and PGE2 in children with PER (n=14) and with PER and concomitant intermittent asthma (IA; n=25), mild persistent asthma (mA; n=28), moderate persistent asthma (MA; n=13) and in Healthy Controls (HCs; n=13). Oral and nasal FENO concentrations were increased in children with PER, IA, mA and MA when compared with HCs. Nasal 8-isoprostane was higher in EBC of children with PER and asthma than in HCs. Oral and nasal LTB4 were higher in EBC of children with PER and mA than in HCs. Oral and nasal PGE2 concentrations were higher in EBC of children with PER than in HCs. Positive correlations between oral and nasal biomarkers were found in IA for LTB4 and PGE2, in mA for FENO, 8-isoprostane, LTB4 and PGE2, and in MA for PGE2. No correlations were observed in children with PER and HCs. Our results suggest that non-invasive markers of inflammation and oxidative stress might be useful to study the relationships between oral and nasal compartments in allergic children with PER and concomitant asthma with the aim of defining the UAD.