In the present work we describe investigations intended to identify the molecular mechanism(s) of H₂O₂-induced cell death. Jurkat cells in culture were treated with either a bolus addition of H₂O₂ or exposed to the enzyme glucose oxidase which generated a continuous flow of H₂O₂. Contrary to the prevailing idea which considers mitochondria as the initial point of action of H₂O₂, we observed that H₂O₂-induced apoptosis is triggered through an initial interaction of H₂O₂ with redox-active iron in the lysosomes. The hydroxyl radicals formed, attacked the lysosomal membranes leading to their destabilization which preceded mitochondrial permeability transition and activation of the caspase cascade. It was also observed that H₂O₂, apart from its well known pro-apoptotic action, could exert anti-apoptotic effects when present, even at relatively low concentrations, during the execution of apoptotic process. In an attempt to identify the exact point of the inhibitory action of H₂O₂, we detected normal formation of the apoptosome complex but inability of caspase-9 to be activated in the presence of H₂O₂. Further experimental work is needed in order to clarify the exact molecular mechanism(s) underlying this observation.