Dieldrin is an organochlorine insecticide highly toxic for human beings. Although its exact mechanism of action is not well known, there is evidence that it acts at the cell membrane level. In fact, the lipophilicity of the pesticide as well as that of the phospholipid bilayer present in biological membranes makes the latter a most likely target for the interaction of dieldrin with living organisms. In order to evaluate its perturbing effect upon cell membranes the pesticide was made to interact with human erythrocytes and molecular models. These studies were performed by scanning electron microscopy on erythrocytes, fluorescence spectroscopy on dimyristoylphosphatidylcholine (DMPC) large unilamellar vesicles and X-ray diffraction on multilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE). It was observed that dieldrin particularly interacted with DMPC liposomes and multilayers perturbing its molecular arrangements. However, no effect was noticed on erythrocytes, which might be due to its high cholesterol content.