Two approaches have generally been used to assessing liver function: one is to measure the products of liver synthesis, the other is to monitor hepatic clearance function. The exogenous dyes that can be used to study liver function are sulphobromophthalein (BSF) and indocyanine green (ICG). One valuable way to measure hepatic function is to use non-toxic substances (stains, sugar, drugs) that are selectively metabolized by the liver and determine the rates of metabolism of these substances in vivo. The antipyrine clearance test is the most common and correlates well with the degree of liver damage. The caffeine clearance test is beneficial in severe liver lesions, but practically useless in the case of moderate liver damage. The galactose clearance test can be used early in the clinical course of jaundice to distinguish between hepatocellular disease and biliary obstruction. The MEGX test is useful as a real-time method for quantitatively assessing pre- and post-transplant liver function. In short, quantitative liver function tests are not suitable for use in screening for liver disease. They are more complex to perform and more expensive than conventional biochemical tests, but superior in monitoring the degree of liver dysfunction.