Objectives: The aim of the study was to determine the level of secondary bile acids (SBA) in the diets and feces of mice and the variation of amount ingested/excreted if these SBA are administered as monotherapy or in 1:1 dose. Methods: The mice were divided into 4 groups and fed for 140 days with different diets. The control lot received a normal diet and the others received diets supplemented with 0.25% deoxycholic acid (DCA), 0.25% lithocholic acid (LCA) and 0.125% DCA+0.125% LCA. After 140 days, the mice feces were collected and homogenized to obtain a mixture for each lot from which the determinations of the studied SBA were performed. For the mice food evaluation, portions of 10 g from each of the 4 diets were subjected to the SBA determination. Results: The daily ingestion over more than 4 months of DCA or LCA added to the diet and administered as monotherapy determine a significantly increase of the SBA eliminated into the feces (the DCA level was 11x higher, and of the LCA 233x higher). If half of the LCA dose is replaced with DCA, the level of LCA in the feces gets comparable with that of the DCA (their combined amounts represents only 13x higher increase of these two bile acids in feces). Conclusions: The simultaneous ingestion and excretion of DCA and LCA can be considered as a particular situation ruled by endogenous mechanisms. This behavior represents an important observation, knowing that the bile acids effects in the colorectal cancer are dose dependent.