Studies on the immediate and long-term effects of radiation on the B-system immunity of children who were affected by radiation after the Chernobyl disaster (from 1986-1992) are summarized in this paper. Complete clinical and immunological examination of more than 6000 children have been carried out. The dynamics of the immune system, with ongoing reactions of cell proliferation and differentiation, gene amplification, transcription, translation, biosynthesis and switching production of isotypes and subclasses of immunoglobulins, as well as specific and nonspecific (natural) antibodies, make it highly susceptible to the action of radiation in addition to other ecological factors. B-system of immunity (B-cel level, concentration of immunoglobulins-M, G, A, E; subclasses of IgG (IgG1-IgG4) in the serum and saliva, and the level of nonspecific heterophilic autoantibodies (RF, antithyroglobulin) were investigated in children of differing ages and sex living in the territories of the Republic of Belarus contaminated with radionuclides. Research showed decreased levels of B-cell and IgM and IgG isotopes 40-50 days after the disaster and increased levels of IgA immunoglobulins at that time. Long-term effects of low doses of radiation showed increased concentrations of IgM and IgG, correlating changes in the B-system of immunity with the level of 137Cs contamination in the territory of residence and also with the amount of 137Cs found in the children.