Electron microscopy gives the real images of individual protein molecules, providing unique means in the structural research of membrane-transport proteins. Various techniques for the preparation of specimens for transmission electron microscopy were briefly described. Emphases were put on the recent progress of quick-freeze cryo-electron microscopy, including cryotransfer and freeze-fracture deep-etch replication. Exploiting the advantage of the latter technique, we visualized the in situ structure of inositol 1,4,5-trisphosphate receptor molecules in the smooth-surfaced endoplasmic reticulum (sER) membrane of the Purkinje neuron in bovine cerebellum. The tetrameric receptor molecules were unexpectedly small and formed a two-dimensional crystalline array on the surface of the cisternal stacks derived from sER. Its structural characteristics were discussed in comparison with the ryanodine-receptor, the other intracellular Ca2+ -channel.