gram-negative bacteria. Lipopolysaccharides are complex glycolipids composed of lipid A, a core polysaccharide, and repeating units of O-specific polysaccharides. Lipid A is associated with the majority of toxic effects of gram-negative bacteria. It interacts with target cells, such as macrophages and activated neutrophils, initiating the inflammatory cascade. The effects of LPS depend mostly on organism reaction to endotoxins, their concentration in blood and also on the state of the animal before the occurrence of endotoxemia. The effect of endotoxin on the reproductive functions of domestic animals has been partly elucidated. This paper presents data on clinical, hematological and biochemical changes in endotoxemia as well as effects of injection of endotoxin in the reproductive systems in boars, rams, and stallions. The results show that these males respond to endotoxins in a similar way, concerning clinical symptoms, body temperature and leukocyte count in blood. Endocrine and seminal changes are different and the range of these changes also depends on the dose and endotoxin exposure time.