Effects of mercury ions on the colonization of mice organs by Listeria monocytogenes were investigated. It was found that single injection of 0.05 LD50 mercury ions has little effect on listeria spreading in mice internal organs. Dissemination of bacteria in the liver of mice, which received 0.5 LD50, was similar to that one in control animals, which received physiologic solution, while higher numbers of bacteria were found in spleen of experimental animals at later stages of infection (after 24 and 48 h), when inflammation processes begin to take place. Chronic exposure to 0.05 LD50 mercury ions for 6 weeks caused decrease in body weight and survival of mice as well as increase in the infection degree of their internal organs. In addition, we demonstrate the mercury ions results in decreased synthesis of specific antibodies against listeria proteins.