The effects of the chaotrophic anion perchlorate (ClO₄ ^–) on glucose-induced electrical activity, exocytosis and ion channel activity in mouse pancreatic B-cells were investigated by patch-clamp recordings and capacitance measurements. ClO₄ ^– stimulated glucose-induced electrical activity and increased the action potential frequency by 70% whilst not affecting the membrane potential when applied in the presence of a subthreshold concentration of the sugar. ClO₄ ^– did not influence ATP-dependent K (K_ATP) channel activity and voltage-gated delayed K⁺ current. Similarly, ClO₄ ^– had no effect on Ca²⁺-dependent exocytosis. The stimulation of electrical activity and insulin secretion was instead attributable to an enhancement of the whole-cell Ca²⁺ current. This effect was particularly pronounced at voltages around the threshold for action potential initiation and a doubling of the current amplitude was observed at –30 mV. This was due to a 7-mV shift in the gating of the Ca²⁺ current towards negative voltages. The action of ClO₄ ^– was more pronounced when added in the presence of 0.1 mM BAY K8644, whereas no stimulation was observed when applied at a maximal concentration of the agonist (1 mM). Single-channel recordings revealed that the effect of ClO₄ ^– on whole-cell currents was principally due to a 60% increase in the mean duration of the long openings and the number of active channels. We propose that ClO₄ ^– stimulates insulin secretion and electrical activity by exerting a BAY K8644-like action on Ca²⁺ channel gating.