- Background Pediatric ALL patients are subjected to an aggressive and continuous chemotherapy protocol, while solid tumor patients have a less intensive treatment. We studied the antioxidant status of children from the two groups and hypothesized that the antioxidant status will differ in concert with their treatment. Procedure The antioxidant status in plasma of seven ALL children and that of six children treated for different solid tumors, in regard to the different treatment regimen, was compared with healthy controls. These samples were taken during therapy, just before the next cyclophosphamide treatment, to determine the accumulative oxidative stress. Results Children from the ALL group (n = 7) had significantly lower thiol plasma levels than controls (P < 0.01) and their antioxidant capacity as measured by the ferric reducing ability of plasma (FRAP) was significantly lower (P < 0.01). These parameters were normal in the solid tumors group (n = 6) but plasma antioxidant capacity as measured by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was significantly lower (P < 0.01). Conclusions Both groups had impaired plasma antioxidant status. The higher oxidative stress of children with ALL is associated with the protocol for treating ALL which is much more aggressive and frequent than that of the solid tumors. The lower antioxidant status in plasma with ALL children is probably associated with increased reactive oxygen species (ROS) as indicated by the decrease of the antioxidant activity. This oxidative stress may lead to cell death or greater sensitivity of the tumor cell to therapy, with better outcome for pediatric patients with ALL. Pediatr Blood Cancer 2008;51:613–615. © 2008 Wiley-Liss, Inc.