Bile acids (BA) play a vital physiological role in vivo. They are not only detergent of dietary lipids and nutrients, but also important hormones or nutrient signaling molecules in metabolic regulation process. Recent studies have also shown BA involvement in various cancers and diseases such as Parkinson's and Alzheimer's and liver diseases. However, majority of the reported literature about BA is restricted to enterohepatic circulation. Hitherto, there has been no comprehensive study of the BA profile in all the major tissue and biofluids in rat has been reported. In this first bileomics study, BA profile of 14 different rat biological specimens (liver, serum, kidney, heart, stomach, ovary, mammary, uterus, small intestine, big intestine, spleen, brain, feces and urine) were studied by ultra-performance liquid chromatography (UPLC)-tandem mass spectrometry (MS/MS). Here I report the comprehensive identification and measurements of bile acids, the bileome, in rat. PCA analysis show distinct separate clusters of tissues as well as biofluids based on BA composition profile. Furthermore, we found that BA profiles of the organs that are involved in enterohepatic circulation were different than the other organs. Most of BA in brain, spleen, heart, ovary, urine, feces and uterus were in the unamidated form, and LCA and MOCA are the most abundant BAs in these organs. Whereas, most of BAs in liver, serum, mammary, large intestine, small intestine, stomach and kidney existed in amidated form, and TCA and T-beta-MCA are primary BAs. Finally, first time, BAs are found and measured in kidney, heart, stomach, ovary, mammary, uterus, and spleen of rats. (C) 2020 Elsevier Inc. All rights reserved.