Iron accumulation in Alzheimer's disease (AD) is linked to the generation of free radicals, which contribute to oxidative damage. This study investigated whether iron, a key source of the hydroxyl radical via the Fenton reaction with hydrogen peroxide (H₂O₂), plays a role in AD pathology. Using a modified histochemical technique, redox-active iron was found associated with senile plaques and neurofibrillary tangles, the hallmark lesions of AD. This iron can participate in in situ oxidation and catalyze H₂O₂-dependent reactions. Deferoxamine, an iron chelator, effectively removed iron from these lesions, which could be rebound after treatment with iron(III) citrate and iron(II) chloride. The binding of iron to these lesions was dependent on histidine residues and protein conformation. These findings suggest that iron accumulation may contribute to oxidative damage in AD. The study also showed that iron is not bound to normal iron-binding proteins but rather to abnormal protein constituents of the lesions. The presence of redox-active iron in these lesions, along with evidence of oxidative stress, supports the role of oxidative damage in AD pathogenesis. The distribution of iron between oxidation states (Fe²⁺ and Fe³⁺) depends on the availability of reducing species and the nature of protein coordination sites. The study highlights the potential for iron to catalyze free radical generation, which could contribute to the oxidative damage observed in AD. The findings are supported by the presence of elevated serum levels of the iron-binding protein p97 in AD patients, suggesting that iron homeostasis alterations may manifest in peripheral markers. Overall, the study indicates that iron accumulation is a significant contributor to oxidative damage in AD.Iron accumulation in Alzheimer's disease (AD) is linked to the generation of free radicals, which contribute to oxidative damage. This study investigated whether iron, a key source of the hydroxyl radical via the Fenton reaction with hydrogen peroxide (H₂O₂), plays a role in AD pathology. Using a modified histochemical technique, redox-active iron was found associated with senile plaques and neurofibrillary tangles, the hallmark lesions of AD. This iron can participate in in situ oxidation and catalyze H₂O₂-dependent reactions. Deferoxamine, an iron chelator, effectively removed iron from these lesions, which could be rebound after treatment with iron(III) citrate and iron(II) chloride. The binding of iron to these lesions was dependent on histidine residues and protein conformation. These findings suggest that iron accumulation may contribute to oxidative damage in AD. The study also showed that iron is not bound to normal iron-binding proteins but rather to abnormal protein constituents of the lesions. The presence of redox-active iron in these lesions, along with evidence of oxidative stress, supports the role of oxidative damage in AD pathogenesis. The distribution of iron between oxidation states (Fe²⁺ and Fe³⁺) depends on the availability of reducing species and the nature of protein coordination sites. The study highlights the potential for iron to catalyze free radical generation, which could contribute to the oxidative damage observed in AD. The findings are supported by the presence of elevated serum levels of the iron-binding protein p97 in AD patients, suggesting that iron homeostasis alterations may manifest in peripheral markers. Overall, the study indicates that iron accumulation is a significant contributor to oxidative damage in AD.