In iron deficiency, serum levels of ferritin decrease. The lack of iron has been thought to be the main factor in this decrease, but another potential factor is nitric oxide, which has been shown to affect ferritin metabolism in vitro. The aim of this study was therefore to evaluate in children with iron deficiency the relation of serum ferritin, nitric oxide degradation products (nitrate and nitrite), and endothelin-1, a protein closely related to nitric oxide function. A total of 80 children were included in the study (39 with iron deficiency, 41 controls). Serum levels of ferritin, nitrate, nitrite, and endothelin-1 were measured in all participants. In children with iron deficiency, nitrate and nitrite levels were significantly higher (p <.009 and .01, respectively). Also, serum ferritin was negatively correlated with serum levels of nitrate and nitrite (p = .034, r = -.254 for nitrate and p = .01, r = -.593 for nitrite). No statistical relationship was found between serum ferritin and endothelin-1.