The effects of methamphetamine (METH) on pro-oxidant processes and on the production of reactive oxygen species were examined in vivo in the rat brain. The presence of oxidative damage in striatum, as revealed by the oxidation of lipid, also was assessed via the measurement of the lipid peroxidation product malonyldialdehyde. To elucidate further the mechanisms mediating METH-induced oxidative stress, we studied the possible reversal of the long-term METH-induced decrease in striatal dopamine content by antioxidants through iron chelation and trapping of free radicals. The uric acid concentration in the striata of rats killed 1 hr, but not 24 hr, after a four-injection regimen of METH was increased significantly compared with saline-injected control rats. METH increased the in vivo formation of the hydroxylated products of salicylate and d-phenylalanine, as evidenced by the elevated extracellular concentrations of 2,3 dihydroxybenzoic acid and p-tyrosine, respectively. The local perfusion of the striatum with the iron chelator deferroxamine attenuated the long-term depletions of striatal dopamine content produced by METH. In other experiments, malonyldialdehyde concentrations in incubated striatal homogenates were elevated significantly in METH-treated rats. Finally, pretreatment with the spin trapping agent phenylbutylnitrone before the METH injections attenuated the subsequent long-term depletions in striatal dopamine content. Overall, the results illustrate that METH increases pro-oxidant processes and offer supportive evidence that METH produces oxidative damage. These studies also demonstrate that iron may be involved in mediating the long-term damage to dopamine neurons after repeated administrations of METH.