Insulin secretion is triggered by a rise in the intracellular Ca²⁺ concentration that results from the activation of voltage‐gated Ca²⁺ channels in the β‐cell plasma membrane. Multiple types of β‐cell Ca²⁺ channel have been identified in both electrophysiological and molecular biological studies, but it appears that the L‐type Ca²⁺ channel plays a dominant role in regulating Ca²⁺ influx. Activity of this channel is potentiated by protein kinases A and C and is inhibited by GTP‐binding proteins, which may mediate the effects of potentiators and inhibitors of insulin secretion on Ca²⁺ influx, respectively. The mechanism by which elevation of intracellular Ca²⁺ leads to the release of insulin granules is not fully understood but appears to involve activation of Ca²⁺/calmodulin‐dependent protein kinase. Phosphorylation by either protein kinase A or C, probably at different substrates, potentiates insulin secretion by acting at some late stage in the secretory process. There is also evidence that small GTP‐binding proteins are involved in regulating exocytosis in β cells. The identification and characterisation of the proteins involved in exocytosis in β cells and clarification of the mechanism(s) of action of Ca²⁺ is clearly an important goal for the future. © 1994 Wiley‐Liss, Inc.