This study was designed to compare the levels of dityrosine-containing protein cross-link products, also known as advanced oxidation protein products (AOPP); in patients with allergic rhinitis with those in healthy individuals considering the fact that AOPP has the potential to be a marker of oxidative stress specific to proteins in mammalian systems. This study was performed on 40 patients (18 males, 22 females; mean age 29 years; range 10 to 53 years) with allergic rhinitis admitted to our clinic between December 2008 and January 2009 and on 40 healthy volunteers (16 males, 24 females; mean age 31 years; range 13 to 48 years). Skin prick test was performed to establish a diagnosis of allergic rhinitis in patients with major symptoms and allergic sensitization was also supported with serum IgE levels. Blood samples were obtained and examined in all patients to determine AOPP. Serum AOPP levels were significantly higher in patients with allergic rhinitis (169.0+/-14.2 micromol/L) compared to controls (43.9+/-3.5 micromol/L; p<0.001). In addition, mean serum IgE levels of patients with allergic rhinitis (308.2+/-38.5 IU/ml) were found to support the presence of allergic sensitization. Determining the levels of serum AOPP, a well-known marker of protein oxidation, appears to be a useful method in determining the role of oxidative stress in the etiopathogenesis of allergic rhinitis.