TBA 21 FS liquid-stable, ready-to-use assay is applicable for total bile acids (TBA) determination in human stool, human serum and plasma and is conveniently applicable on automated analyzers, which are technically established in clinical laboratories and highly timesaving. It has a wide measuring range (up to 130 µmol/L), good precision and long onboard and calibration stability, and also shows minimized interferences by standard stool components as well as a good reproducibility.