PRESENT-DAY histochemical methods for demonstrating cholinesterases require the use of inhibitors in order to distinguish between acetyl- (that is, true, or specific) cholinesterase (AChE) and butyryl- (non-specific) cholinesterase (ChE). The histochemical technique determines AChE and ChE together, so that if either enzyme is inhibited without the other being affected, only the latter can be determined; thus an inhibitor of ChE makes it possible to determine AChE and vice versa.