Recent reports implicating anticholinesterase agents in the production of lens opacities have led us to look for the target of these agents, that is, the enzyme cholinesterase, in the lens. A form of cholinesterase, sensitive to low concentrations of eserine, has been found. This is true cholinesterase as indicated by inhibition of enzymatic activity with high substrate concentrations and by the enzyme's hydrolysis of acetylthiocholine more rapidly than the longer chain propionyl or butyryl analogues. The enzyme is localized near the lens surface, either within or closely bound to the lens capsule. The physiologic role of the enzyme is unknown.