15 acetoxyethylenammonium compounds are studied as substrates for acetylcholinesterase (ACE) from bovine erythrocytes and for butyrylcholinesterase (BCE) from horse serum. Substitution of methyl groups of the ammonium grouping with other radicals and incorporation of onium nitrogen in the cycle resulted in the decrease of the hydrolysis rate under the action of BCE and ACE, the effect of BCE being more pronounced. The rate of the hydrolysis of N-acetoxyethylene-N-methylpiperidine iodide in the presence of ACE was 65 times as much as in the presence of BCE. This compound is a new specific substrate of ACE. Dipropylmethyl derivative turned not to be a good substrate for both enzymes. Dibutylmethyl and pyridinic derivatives were not attacked by ACE and BCE. Kinetic analysis of the compounds listed is performed, taking account of non-productive sorbtion. Possible role of hydrofobic regions in the orientation of substrates on the active surface of ACE and BCE is discussed.