High density lipoproteins (HDLs) play a critical role in cholesterol metabolism and their plasma concentrations are inversely correlated with risk for atherosclerosis. SR-BI and SR-BII (previously known as SR-BI.2) are the alternatively spliced products of a single gene. SR-BII and SR-BI are identical except for the encoded c-terminal cytoplasmic domain. Both SR-BI and SR-BII bind HDL and mediates selective uptake of HDL cholesteryl ester, but with SR-BII having an approximately 4-fold lower efficiency than SR-BI. SR-BI and SR-BII are expressed primarily in liver and non-placental steroidgenic tissues. Although the role of these scavenger receptors is not completely clear, SR-BII mRNA results from the alternative splicing of SR-BI precursor transcripts with both isoforms mediating selective transfer of lipid between HDL and cells. Therefore, the relative expression and functional activities of these two isoforms create a potential means of regulating selective lipid transfer between HDL and cells.