The invention relates to 4-oxo-2,3,4,5-tetrahydro-benzo [b][1,4]diazepines of formula I ##STR00001## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are as defined in the description and claims, which are .gamma.-secretase inhibitors and which may be useful in the treatment of Alzheimer's disease.