Membrane conductance activated by acetylcholine (ACh-conductance) was studied in rat isolated superior cervical ganglion neurons by means of the patch-clamp method in the whole-cell recording mode. It was found that ACh-conductance was increased or decreased with membrane hyper- or depolarization, respectively. The decrease in ACh-conductance was not associated with the reversal of ACh-current or with the presence of Ca2+ ions in external solution. The time constant of voltage-jump relaxation of ACh-current revealed e-fold increase with membrane hyperpolarization by 70 mV, which corresponded to the voltage dependence of ACh-conductance. Basing upon these results it was concluded that the voltage dependence of ACh-conductance is mostly determined by the voltage dependence of nicotinic receptor channel gating kinetics.