This article is devoted to a topical issue of current-day medicine, which is endogenous intoxication. In this article you can find an analytical review of scientific sources about types and stages of endogenous intoxication, significance of medium mass molecules (MMM) as an integral indicator of endotoxicosis. Methodological approaches to the determination of MMM in biological fluids are reviewed. The results of scientific studies on the measurement of the level of MMM in animals are described, which indicate the pros-pects for the analysis of markers of endogenous intoxication for practical usage in veteri-nary medicine. The research on the level of MMM may help improve the diagnosis of pat-hological processes in the animal's body, and will also allow you to identify the direction of the course of the disease in order to improve therapeutic and preventive measures and evaluate their effectiveness.