Alzheimer's disease is characterized by the abnormal aggregation of amyloid-β (Aβ)1-40 and Aβ1-42 peptides into fibrils. In this work, we analyzed the kinetics of Aβ1-40 and Aβ1-42 fibril formation in vitro using Thioflavin T fluorescence. We synthesized high-purity peptides and performed a hexafluoro-2-propanol pre-treatment to yield uniform peptide solutions as starting materials. We found that the aggregation is clearly affected by the presence of sub-millimolar quantities of antibodies against the C-terminal region of the peptides. Because the fibrillization of these peptides is closely related to the pathogenesis of Alzheimer's disease, blocking this process may provide significant therapeutic benefit.