At room temperature micro-injections of calcium or strontium produced transient hyperpolarizations with an associated rise in input conductance. By contrast micro-injections of potassium, barium, magnesium, cobalt or lanthanum did not produce hyperpolarizations. The reversal potential for the hyperpolarizing response was about -80 mV. Some responses to calcium injections appeared to suffer from an additional transient leak conductance generated by the injected current. In these cases the recovery of the potential and the conductance to normal values was prolonged. The reversal potential of this additional leak pathway was about -10 mV. Experiments designed to investigate the role of active calcium extrusion from the cells showed that extracellular lanthanum or quercetin caused a pronounced slowing of the recovery phase of the potential and conductance response to calcium injection. The metabolic uncoupler dinitrophenol also prolonged the calcium-evoked responses. The replacement of extracellular sodium by lithium or choline produced no alteration in the time course of the calcium-evoked responses, thus suggesting that sodium-calcium exchange exerts no rate control on the recovery phase of those responses.