It is supposed that ENM toxicity is based on oxidative stress, although the exact mechanism how nanoparticles induce formation and generation of reactive oxygen species (ROS) is not completely understood. Toxicity of nanoparticles depends on their properties and rout of entrance in the body, concentration and duration of exposure to nanoparticles, but also on individual susceptibility and state of organism. Results when oral route of transmission was studied showed that signs of toxicity were noted only with relatively high doses of nano-silver or nano-TiO2 applied