It is established that derivatives of polymethylene bistrimethylammonium (CH3)3N+(CH2)nN+(CH3)3 (n = 4-10) are reversible competitive and mixed action inhibitors with respect to acetylcholinesterase of human erythrocytes, butyryl cholinesterase of horse blood serum, cholinesterase of frog brain and Todarodes pacificus optical ganglion. In case of mammals and frog cholinesterase the inhibitors efficiency rises with n, but the activity of the Todarodes pacificus cholinesterase less sensitive of the inhibitors is characterized by a "step" dependence on the length of the polymethylene chain of the inhibitor molecule. Studies in sensitivity of cholinesterases to this type of inhibitors revealed differences between enzymes of the same type in different animals.