Cholesterol, particularly in the form of low density lipoproteins (LDL), is well understood to be associated with increased risk of coronary heart disease. The measurement of cholesterol is one of the most common tests performed in the clinical laboratory setting. However, simple and easy assays for cholesterol in the research lab have not been readily available. Cayman"s Cholesterol Fluorometric Assay provides a simple fluorometric method for the sensitive quantitation of total cholesterol in plasma or serum. In our assay, cholesteryl esters in the sample are first hydrolyzed by cholesterol esterase. All cholesterol, whether previously esterified or existing free in the circulation, is then oxidized by cholesterol oxidase to the corresponding ketone and hydrogen peroxide. ADHP (10-acetyl-3,7-dihydroxyphenoxazine) is utilized as a highly sensitive and stable probe for hydrogen peroxide. Horseradish peroxidase catalyzes the reaction of ADHP with hydrogen peroxide to yield the highly fluorescent product resorufin which can be monitored using excitation wavelengths of 530-540 nm and emission wavelengths of 585-595 nm.