Human butyrylcholinesterase (BChE) has long been studied as a potential scavenger of nerve agents. Upon inhibition, the enzyme is covalently modified and the nerve agent is completely destroyed. Recently, human BChE has been the target of the development of new molecules for the treatment of the late stage of Alzheimer's disease. We propose to determine the structures of human BChE in complexes with such ligands. These structural pieces of information will both help to improve the anti-Alzheimer's molecules and also to design new BChE-specific strong nucleophiles named reactivators in order to treat nerve agent intoxication.