Objective: The prevalence of allergic asthma is increasing on a global scale, reflecting changes in air pollution, climatic changes, and other environmental stimulants. In allergic conditions, oxidative stress occurs as a result of immune system activation. Oxidation of cholesterol leads to the formation of oxysterols. The main purpose of the study was to compare plasma levels of two oxysterols, namely 7-ketocholesterol (7-KC) and cholestane-3 beta, 5 alpha, 6 beta-triol (C-triol), and a lipid peroxidation product, malondialdehyde (MDA) in allergic asthma patients with those of healthy controls, in order to provide information about the involvement of lipid peroxidation in allergic asthma. Methods: Oxysterols were quantified by LC-MS/MS in plasma samples of 120 asthma patients (90 females + 30 males) and 120 healthy controls (matched by age and sex). Plasma MDA level was analyzed by a spectrophotometric method. Results: Plasma 7-KC (39.45 +/- 20.37 ng/mL) and C-triol (25.61 +/- 10.13 ng/mL) levels in patients were significantly higher than in healthy subjects (17.84 +/- 4.26 ng/mL and 10.00 +/- 3.90 ng/mL, respectively) (P < 0.001). Plasma MDA levels were also higher in asthmatic patients (4.98 +/- 1.77 nmol/mL) than in healthy controls (1.14 +/- 0.31 nmol/mL) (P < 0.001). All data support that lipid peroxidation products are involved in allergic asthma. Conclusion: Oxysterols were quantified for the first time in allergic asthma. Since the high plasma 7-KC and C-triol levels of allergic asthma patients correlate with high IgE levels, detection of these oxysterols by LC-MS/MS may be helpful in the clinical monitoring of allergic asthma. Current data may also lead to new approaches for the prevention, diagnosis, and treatment of the disease. Supplemental data for this article is available online at at.