BACKGROUND Dengue is a major cause of morbidity in tropical and subtropical regions. It has been shown that there is a relationship between immune and oxidative mechanisms leading to altered immune responses. The role of free radicals in the pathogenesis of dengue fever in children is lacking. Aim-This study was done with the objective of determining various oxidants and antioxidants and evaluating their role in pathogenesis of severe form of Dengue Fever, Dengue Haemorrhagic Fever. MATERIALS AND METHODS 30 patients with Dengue Haemorrhagic Fever (DHF) in the age group of 0-16 years, having clinical features of DHF and positive findings in blood test were included in this study. Another 30 age and gender-matched children were included in this study to serve as controls. Levels of plasma MDA, protein carbonyl, nitrite, H2O2 and MPO activity were estimated by different standard methods. Statistical analysis was done with the help of t-test. Settings-This study was done in Mayo Institute of Medical Sciences, Lucknow. Design-A prospective, institution-based study. RESULTS The mean age of presentation of children with DHF was comparable to control values. The mean plasma levels of MDA, protein carbonyl, nitrite, Cu, H2O2 and MPO activity were significantly higher in patients with DHF as compared to control values (p < 0.05 each). CONCLUSION It can be concluded that imbalances between prooxidants and antioxidants play a significant role in pathogenesis of children with DHF.