Scientists have found that some potential beta-secretase inhibitors such as semagacestat, which have been used in large clinical trials that ended in failure, do not function as true inhibitors as originally expected, but rather cause accumulation of toxic intraneuronal A?. They proved this by introducing an original method to measure direct intracellular products of beta-secretase. They commented that the application of their evaluation method may help develop truly effective drugs for Alzheimer’s disease (AD).