Serum total bile acid (TBA) levels are a sensitive marker of liver function and may be used for diagnosis and monitoring of various liver diseases. Increased serum TBA levels are associated with diseases such as acute and chronic hepatitis, intrahepatic cholestasis of pregnancy (ICP), liver sclerosis, cirrhosis, and cancer; TBA may as well detect hepatic dysfunction. Conventional liver tests such as ALT and AST cannot provide this because they are indicators for hepatocellular integrity. TBA measurement corresponds to the sum of more than 20 individual bile acids synthetized by the liver, modified by gut bacteria, and involved in complex enterohepatic circulation. Commercially available assays show limitations regarding the detection of individual primary and secondary bile acids. The new DiaSys reagent, Total bile acids 21 FS, is an enzyme cycling assay which enables assessment of all relevant bile acids in a sample and hence offers the possibility to precisely cover all stages of liver diseases. The new liquid-stable, ready-to-use reagent provides a wide measuring range, outstanding precision and shows significantly reduced interferences compared with nitrotetrazolium blue (NBT) methods.