The influence of external pH shifts in the range pH 4.5 to 10 on acetylcholine-induced currents was investigated under voltage clamp conditions in neurons of ‘Helix pomatia’. Observations were limited to neurons which responded to electrophoretic application of acetylcholine with a transient hyperpolarization. The reversal potential for acetylcholine-induced currents was altered very little by pH changes. A decrease or an increase of the peak acetylcholine-induced conductance change was noted on different neurons when pH was shifted away from the physiological value of 7.65. This finding is probably attributable to a nonhomogenous distribution of cholinesterase. pH shifts produced consistent changes in the time course of acetylcholine-induced currents. The average rate of current rise plotted as a function of pH delineates a curve with an optimum at approximately pH 7.65. The implications of our findings as related to the charge distribution on the surface of acetylcholine membrane receptors are discussed.