The relationship between changes in intracellular free calcium concentration (Cai2+) and cell functions is becoming more clear, since it has become possible to measure Cai2+in a living cell. There are, however, still unsolved questions concerning the role of Ca2+in cellular signal transmission. It is not easy to relate Ca2+signalling to the functions of a living cell. It is possible to control the amount of Ca2+using calcium channel blockers, but it is still almost impossible to elucidate the relationship between Ca2+and cellular functions by controlling Ca2+signalling.One approach to solving this problem is to develop and use protein kinase inhibitors. Inhibitors specific to Ca2+/calmodulin‐dependent protein phosphorylation, which is one of the important network systems of the Ca2+signalling, attract interest among many researchers. The substances that can control Ca2+signalling include: 1) calcium channel blockers, 2) calmodulin antagonists, and 3) Ca2+/calmodulin‐dependent protein kinase inhibitors. Each substance has a different site of action.In this article, the action of KN‐62, an inhibitor specific for Ca2+/calmodulin protein kinases (CaM kinases) will be desc