Class B scavenger receptors are predominantly localized to cholesterol and sphingomyelin-enriched domains within the plasma membrane, called caveolae. Caveolae and their associated protein, caveolin, have been implicated in cholesterol trafficking and in the regulation of cellular cholesterol homeostasis. Recent studies indicate that scavenger receptor, class B, type I (SR-BI) mediates cholesterol flux between cells and lipoproteins. Caveolae appear to be the sites within the plasma membrane where such exchange occurs, suggesting that the regulation of caveolae and caveolins may be pivotal to the net flux of cholesterol between cells and lipoproteins when they are bound to SR-BI.