Atopic dermatitis (AD) is a chronic inflammatory skin disease of unknown etiology. To examine the involvement of impaired homeostasis of oxygen/nitrogen radicals in childhood AD, we compared the levels of urinary 8-hydroxy-2'-deoxyguanosine (marker of oxidative stress), nitrite/nitrate (marker of nitric oxide synthesis) and selenium (marker of selenium store) in 27 children with AD to those of 25 healthy control children. Urinary 8-hydroxy-2'-deoxyguanosine was significantly higher and nitrite/nitrate levels were significantly lower in patients with AD than in the control. Urinary selenium levels were similar in both groups. Our findings suggest that impaired homeostasis of oxygen/nitrogen radicals and increased oxidative stress are involved in the pathophysiology of childhood AD, and indicate that suppression of oxidative stress might be a potentially useful strategy for the treatment of AD.