The toxicity of amphetamines is conditioned by a complex array of mechanisms, involving the increase of neurotransmission (e.g. leading to hyperthermia) and enzymatic and non-enzymatic oxidation of amphetamines and biogenic amines. Considering that all these processes may increase the generation of hydrogen peroxide (H2O2) by metabolic or non-metabolic redox pathways, the main objective of this work was to evaluate d-amphetamine-induced H2O2 production in mice liver, kidney and heart. The contribution of monoamine oxidase (MAO) to H2O2 production after d-amphetamine administration was studied using the MAO inhibitor pargyline. H2O2 production was measured indirectly using the catalase-H2O2 complex I irreversible inhibitor 3-amino-1,2,4-triazole (AT). Using this method, the measurement of residual catalase activity following administration of AT permits the monitoring of H2O2 production in vivo. Charles River CD-1 mice (30-35 g body weight) were injected with AT just before the injection of d-amphetamine sulphate (20 mg/kg). d-Amphetamine stimulated the production of H2O2 in all tissues studied, although to different degrees. MAO inhibition by itself led to a remarkable decrease of basal H2O2 production in the kidney and a slight decrease in the liver, although no effect was observed in the heart. d-Amphetamine-induced H2O2 production in the heart and kidney was reduced in MAO-inhibited mice. However, in the liver, H2O2 production was transiently potentiated at 30 min under MAO inhibition. In conclusion, d-amphetamine administration leads to an increase in H2O2 production in mouse liver, kidney and heart, and monoamine oxidase plays an important role in this effect.