The aim of the project is investigation of the effects of environmental agents on important physiological homeostatic system, immune system, of mouse-like rodents. Cellular and molecular mechanisms of immunomodulatory potential of two environmental xenobiotics (ubiquitous pollutant cadmium and anticoagulant warfarin, used for control of pest rodents) is investigated in laboratory populations of Norway rat ( Rattus norvegicus). The effect of these agents on immune system is analyzed using parameters of basal immune activity and in settings of immune response induction as well. Distinct aspect is examination of the impact of these agents on laboratory rat's resistance to opportunistic fungus Aspergillus fumigatus. Wild Norway rats harbor variety of parasites and microorganisms and are thus considered as natural biological models suitable for examination of immune function in settings of multiple infections. Analysis of basic parameters of immune function as well as immune-mediated damage of peripheral tissues of Norway rats from urban environment and comparison with same parameters in several laboratory strains of Norway rats gives insight into the effect of the environment on immunity.