The amyloid β-peptide (Aβ) and aluminum are found, among other components, in the senile plaques of patients with Alzheimer’s disease. Aggregated Aβ and aluminum are toxic to neurons but the mechanism of accumulation and toxicity remains poorly understood. It has been proposed that Aβ and aluminum toxicity results from Aβ– and aluminum–membrane interactions. It was therefore of interest to study the effect that Aβ and aluminum could have on cell membranes. Thus, the interactions of Aβ(1-40), Aβ(1-42), and Al(III) with the human erythrocyte membrane and a molecular model of the erythrocyte membrane were examined by electron microscopy and X-ray diffraction, respectively. The molecular model consisted of bilayers built up of dimyristoylphosphatidylcholine and dimyristoylphosphatidylethanolamine, phospholipid classes located in the outer and inner monolayers of most cell membranes, respectively. Aβ(1-40) and Aβ(1-42) in the presence of Al(III) altered the erythrocyte membrane morphology and the structure of dimyristoylphosphatidylcholine bilayers, effects that were different and stronger than those induced by Aβ and Al(III) separately.