Patients with advanced-stage chronic renal failure (CKD) are exposed to strong oxidative stress, and hemodialysis (HD) is considered to improve this. Multiple reports have been published on this topic, including our previous reports (J Am Soc Nephrol1997). However, recent advances have revealed that the oxidative stress in CKD does not simply increase unidirectionally. By using the newly developed electron spin resonance (ESR)-based analytical methods, we reevaluated the effects of HD on the oxidative status of patients with CKD. Two methods, namely multiple free radical scavenging assay (MULTIS), which evaluates scavenging activities against multiple reactive oxygen species (ROS) using CYPMPO as a spin trap, and iStrap, which is a sensitive method to detect lipid-derived carbon-center radicals using a spin trapDPhPMPO, were used in this study. Thirty-three patients undergoing maintenance HDwere enrolled. Informed consent was obtained before the trial. Thirteen cases were complicated with type 2 diabetes. Confirming our previous result, serum hydroxyl radical scavenging activity was significantly improved after HD. By contrast, scavenging activities against alkoxyl and alkylperoxyl radicals were significantly reduced after HD, which suggests a deterioration of the radical scavenging system downstream of the radical chain reaction. These reductions in scavenging activities were more obvious in patients with diabetes. The changes in the signal intensity of DPhPMPO in the whole tested group varied, whereas that of the diabetic patients was increased after HD, consistent with the alkylperoxyl radical findings. The superoxide scavenging activity was higher in the CKD subjects than that in the non-CKD subjects before HD, which then decreased after HD. These results indicate that the HD process does not simply decrease oxidative stress. Although intensive improvements have been made on the materials used in the HD session, such as the dialyzer membranes, ROS downstream of radical chain reactions are still not adequately controlled.