The effects of amiridine and tacrine on the membrane potential, activity and plasticity of cholinoreceptors have been studied using the recording of intracellular and transmembrane currents in identified neurons of Helix lucorum. Amiridine and tacrine (1-100 mcM) have no noticeable effects on the membrane potential of the cells. Both compounds modulate the activity of cholinoreceptors to judge from their influence on the inward current induced by the local acetylcholine (ACh) application: they increase the duration of the current with a two-phase effect on the amplitude (a short-latent intensification with a following decrease). Amiridine and tacrine intensify ACh current extinction induced by repeated ACh application to the soma. Acetylcholinesterase inhibitor physostigmine has a similar modulating effect on ACh current and its extinction. It impedes the modulating effects of amiridine and tacrine. Amiridine and physostigmine directly affect cholinoreceptors and ion channels controlled by them changing in a similar way the current-voltage curves of ACh-current and approximating it to the equilibrium potential of chloride ions. Modulating effects of amiridine, tacrine and physostigmine on the activity and plasticity of cholinoreceptors may be supposed to be caused by their direct membrane-cytoplasmic action.