Caveolae in the plasma membrane have been a focus of intensive research during the past several years. There has been confusion concerning caveolae and caveola-like membrane domains, but it is now generally thought that the latter is a region distinct from caveolae. However, due to similar buoyancy of caveolae and caveola-like membranes, whether caveolae in situ are enriched with a given molecule is often difficult to be concluded by biochemical techniques alone. Furthermore, relatively shallow caveolae may be detected by some techniques, but not by others. Thus whether a molecule is enriched in caveolae should be confirmed by methods based on different principles. Among many putative caveolar molecules, those related to Ca2+ influx and extrusion were shown to be concentrated in caveolae by both immunocytochemical and biochemical techniques. In conjunction with other characteristics, the result implies that caveolae may function as a mobile compartment for Ca2+ signalling.