The effects of some ammonium compounds diiodomethylate acetate (I), propionate (II), butyrate (III), valeriate (IV) N-hydroxyethylanabasine, tetramethylammonium, tetraethylammonium and acetylcholine amide analog derivatives (V-VIII) on acetylthiocholine hydrolysis by cholinesterase from frog brain, acetylcholinesterase from human erythrocytes and butyryl cholinesterase from horse blood serum were studied. Cholinesterase from frog brain possesses a lower sensitivity to the inhibitors than does the mammalian enzyme. Significant conformational changes of the inhibitor molecule, i. e. transition from trans-conformation (V) to the fixed gosh-conformation (VII), have no effect on the anticholinesterase activity of these compounds. A method for evaluation of effectivity of different types of the reversible inhibitors is proposed.