The aim of the research was to model the experimental infection in laboratory rats with the larvae of the nematodes Eustrongylides excisus and documenting the macroscopic changes in organs and tissues of the animals. With a purpose of creating the best conditions for the nematodes larvae’s survival the animals were divided into 4 groups. The first group included intact animals. The rats of groups II and III were orally given the 1% chlorine hydride solution in the amount of 0.5 and 1 ml respectively. Group IV was a control. The rate of the larvae survival in groups I, II and III counted, respectively, 18, 38 and 52% of the general amount of the larvae put into the organisms of the rats. Among the invaded rats next changes of the clinical conditions were noticed: general weakness, absence of appetite, pain and tension in the abdominal wall etc. After euthanasia and followed autopsy the symptoms of serofibrous (20% of the invaded animals) and fibrinopurulent (66.6%) peritonitis were noticed. It also showed the signs of the enteral failure syndrome (73.3%) and the abdominal layers adhesion (86.6%). Microabscesses under the liver capsule were noticed as well, in 26.6% of the experimentally infected rats. Pathological changes in the thoracic cavity organs, in part in the heart (pericard and heart sac hemorrhages) and in the lungs (congestive hyperemia and pulmonary edema) have been found in 60% cases, and in kidneys in 73.3% cases. Symptoms of catarrhal and hemorrhagic gastritis were observed. The positive correlative connection between the parasitic survival percentage in the organisms of rats and the depth and difficulty of the pathological process was determined.