The enzyme β-secretase (BACE1) remains an important potential disease-modifying target for developing drugs to treat Alzheimer's disease. However, finding selective BACE1 inhibitors that can penetrate the brain has proved challenging. In this issue of Science Translational Medicine, a pair of studies describes a new approach to inhibiting BACE1 using a human monoclonal antibody that uses receptor-mediated transcytosis to cross the blood brain barrier (Atwal et al. and Yu et al.). The authors engineer a low-affinity bispecific monoclonal antibody targeting both BACE1 and the transferrin receptor and show that this antibody enters the brain more readily and inhibits BACE1 activity more efficiently than does a monospecific antibody against BACE1 alone. These findings should stimulate attempts to use receptor-mediated transcytosis to increase brain uptake of therapeutic antibodies for a variety of brain disorders.