Amyloid β-Peptide (1-40) (human) is a 40-residue protein fragment of the C-terminal portion of the β-amyloid protein, which is found in plaques in the brains of patients with Alzheimer’s disease. It is neurotrophic and neurotoxic in vivo and in vitro in human and rat neuronal cell cultures. It prevented neuronal cell death by inhibiting fibril formation when administered concurrently with Aβ (1-42) in rat cortical cultures at 3 µM. It prevented neuronal damage when injected into rat entorhinal cortex with Aβ (1-42) both at 400 µM.