Background: Patients with asthma generate an increased amount of reactive oxygen species from peripheral blood cells, which may contribute to its pathogenesis. Saliva analysis is non-invasive and friendly to children. We undertook this study to analyze the salivary oxidative profile and composition in children with asthma during attack and remission, and to compare them with the levels of salivary antioxidants of healthy control children. Methods: School age (range 6-18 years) children referred to the emergency room for acute asthma were included. Clinical score was assessed, spirometry performed, and saliva samples were collected and analyzed. All measurements were repeated during remission of asthma attack (2-4 weeks after attack). Salivary analysis was performed blindly during asthma attack and the results were compared to those obtained during remission, and to those of the control group. Results: Statistically significant decreases in levels of salivary peroxidase enzyme activity were observed in asthmatic children during attack compared with healthy controls, with partial recovery during remission of attack. Similarly decreased levels of calcium concentrations were observed in asthmatic children, accompanied by increased phosphate levels. Conclusions: Children with acute asthma attacks exhibit a decrease in the activity of the most important salivary antioxidant enzyme-peroxidase, which is accompanied by other salivary composition alterations. Hence, acute asthma is manifested by salivary changes. This implies systemic oxidative stress in asthma, which may be reflected in salivary analysis. (c) 2005 Elsevier Ltd. All rights reserved.