tThis paper concerns the studies towards membrane-damage effect of two auxins: indole-3-acetic acid– IAA and 1-naphthaleneacetic acid – NAA on plant (Arabidopsis thaliana) and animal (rat liver) modelmembranes. The foregoing auxins are plant growth regulators widely used in agriculture to control thequality of the crop. However, their accumulation in the environment makes them hazardous for theliving organisms. The aim of our investigations was to compare the effect of natural (IAA) vs. synthetic(NAA) auxin on the organization of plant and animal model membranes and find a possible correlationbetween membrane-disturbing effect of these compounds and their toxicity. The collected data evidencedthat auxins cause destabilization of membranes, decrease their condensation and weakens interactionsof molecules. The alterations in the morphology of model systems were also noticed. The foregoingeffects of auxins are concentration-dependent and additionally NAA was found to act on animal vs. plantmembranes more selectively than IAA. Interestingly, both IAA and NAA induce the strongest disorderingin model lipid system at the concentration, which is frequently reported as toxic to animal and plants.Based on the above findings it was proposed that membrane-damage effect induced by IAA and NAA maybe important from the point of view of the mechanism of toxicity of these compounds and cannot beignored in further investigations in this area.