Scavenger receptor class B member 1 (SRB1), also known as SR-BI, is a protein that in humans is encoded by the SCARB1 gene. SR-BI functions as a receptor for high-density lipoprotein. Scavenger receptor class B, type I (SR-BI) is an integral membrane protein found in numerous cell types/tissues, including the liver and adrenal. It is best known for its role in facilitating the uptake of cholesteryl esters from high-density lipoproteins in the liver. This process drives the movement of cholesterol from peripheral tissues towards the liver for excretion. This movement of cholesterol is known as reverse cholesterol transport and is a protective mechanism against the development of atherosclerosis, which is the principal cause of heart disease and stroke. SR-BI has also been identified in the livers of non-mammalian species (turtle, goldfish, shark, chicken, frog, and skate), suggesting it emerged early in vertebrate evolutionary history. The turtle also seems to upregulate SB-RI during egg development, indicating that cholesterol efflux may be at peak levels during developmental stages.