Proteolytic cleavage of amyloid-β-protein precursor (AβPP) by β- and γ-secretases results in production of the amyloid-β peptide (Aβ) that accumulates in the brains of sufferers of Alzheimer's disease (AD). We have developed a monoclonal antibody, 2B12, which binds in the vicinity of the β-secretase cleavage site on AβPP but does not bind within the Aβ region. We hypothesised that this antibody, directed against the substrate rather than the enzyme, could inhibit cleavage of AβPP by β-secretase via steric hindrance and thus reduce downstream production of Aβ. The antibody would enter cells by binding to AβPP when it is at the cell surface and then be internalised with the protein. We subsequently demonstrated that, after addition of 2B12 to standard growth media, this antibody was indeed capable of inhibiting Aβ40 production in neuroblastoma and astrocytoma cells expressing native AβPP, as measured by an ELISA. This inhibition was both concentration- and time-dependent and was specific to 2B12. We were only able to inhibit approximately 50% of Aβ40 production suggesting that not all AβPP is trafficked to the cell surface. We propose that this antibody could be used as a novel, putative therapy for the treatment of AD.