The mechanism by which the expression of pro-apoptotic protein Bax is able to kill yeast was investigated. Ethanol stress induces a permeabilization of the plasma membrane revealed by propidium iodide accumulation. Bax expression, although killing yeast cells, prevents this permeabilization. These effects are modulated by aeration, by manipulation of the unsaturation index of fatty acids and by addition of resveratrol, a known inhibitor of lipid oxidation. These data suggest that lipid oxidation is involved in Bax effects. Taken together, these data show for the first time a direct effect of Bax on plasma membrane permeability properties and suggest that yeast is a powerful tool for investigating the molecular mechanisms underlying this process.