Caveolae are 50～100 nm membrane micro-invaginations associated with the plasma membrane of a variety of cells. They were first identified in transmission electron micrographs 40 years ago. Functionally, caveolae are thought to participate in transcellular transport of both small and large molecules across capillary endothelial cells. In addition, caveolae have been postulated to function in potocytosis. More recently, there is growing evidence that caveolae also participate in transmembrane signal transduction.