Summary: Procedure used to determine the total concentration of cholesterol present in blood, serum, and plasma. Cholesterol esters are hydrolysed by cholesterol esterase. Cholesterol is then oxidized by cholesterol oxidase with formation of hydrogen peroxide. Peroxidase uses the hydrogen peroxide, phenol, and 4-aminotipyrine to form a quinoneimine dye which is measured at 500 nm.