Chaga’s disease constitutes a serious public health problem affecting approximately 20 million people in South and Central America. Drugs that prevent or cure this disease have not been found yet. As an intracellular parasite, T. cruzi, the ethiologic agent, is exposed to reactive oxygen species (ROS), which arise from a number of different mechanisms, including those generated from its own aerobic metabolism, drugs and by the host immune response. T. cruzi has an effective but complex system to deal with hydroperoxides, converging to the unique trypanossomatid protein trypathione that is absent in the mammalian host. The objective of this work was to analyse the effect of hydrogen peroxide in T. cruzi oxygen consumption and mithocondrial membrane potential (DY). Determinations were made using a Clark eletrode for oxygen consumption and safranine in a Fluorimeter (HITACHI F4500) for DY measurement (EX: 495 and EM: 586nm).  Two different strains (Y and Tulahuen 2) with different resistance to the oxidative stress generated by hydrogen peroxide (IC₅₀=98,54±1,66 mM and 133,09±2,09 mM, respectively) were compared. Oxygen consumption, with endogenous substrate, was the same in both strains (0.88 nmoles of oxygen consumption / 10⁷ cells / min). When cells were incubated in the presence of 50μM of hydrogen peroxide, oxygen consumption decreased in approximately 53% and 77% in Tulahuen 2 and Y strains, respectively.  Y cells were more sensitive to digitonin treatment requiring a smaller concentration for plasmatic membrane permeabilization. Digitonin in the concentration of 15μM allowed the determination of the mitochondrial membrane potential in both strains.  No significative changes were observed in Tulahuen 2 cells treated with either 50mM or 65mM H₂O₂.  However when Y cells were submitted to the same treatment an increased membrane permeabilization to safranine and loss of mitochondrial membrane potential were observed.  The results demonstrated that hydrogen peroxide treatment affects mitochondrial functions at different levels correlated to resistance to the oxidative stress generated.