The power of chosen carbamates and hydrazinium derivatives (carbazates) to inhibit the hydrolysis of acetylthiocholine by butyrylcholinesterase or acetylcholinesterase was tested. The determined pI50 values (= negative logarithm of the molar concentration inhibiting the enzyme activity by 50%) of the tested substances were compared with pI50 values of the commercially used drugs for the Alzheimer's disease treatment--rivastigmine and galanthamine.