Malignant neoplasms (MN) have been found to develop most frequently in the liquidators of entry into the ChNPP zones in 1986 (43.75%), as well as among the liquidators who worked for long, one quarter of whom participated in liquidation of the consequences of failure (LCF) in 1986. Specific features of the immune status depending on the timing of participation in LCF and the year of entry into the ChN PP zone have been established. Changes in the immune system in the persons with a confirmed diagnosis of MN who took both a non-permanent and permanent part in liquidating the consequences of the ChNPP failure in 1986 had the same character of deviations and differed in the magnitudes of deviations of immunological parameters. Continuous participation in the period of extreme conditions and a greater exposure to the radiation factor led to the increased content of CD8(+)-T-cells, CD16(+)-lymphocytes and activated T-lymphocytes, as well as to the reduced index of immune regulation, decreased content ofCD3-16/56+(NK)-cells (%) and the total IgE and to a greater deficiency of B-lymphocytes. Distinctions in the groups of liquidators who participated in LCF in 1986 and 1987 have been revealed. The greatest deviations in the IS indicators were found in liquidators-87. A similar effect came to light in case of a continuance in the ChNPP zones in 1986 and 1987; however, the degree of deviation of the content of CD4(+)-T-lymphocytes (41), CD8(+)-T-lymphocytes (1) and the immune regulation index (41) were remarkably higher in liquidators-87. A continuous stay in the ChNPP zones in 1987 led to the deficiency of CD4(+)-T-lymphocytes, increased values of CD8(+)-T-lymphocytes, a decreased index of CD4+/CD8+, as well as to the change in the ratio between NK-T and NK cells, increased numbers of CD95+, HLA-DR+ and activated T-lymphocytes, and a lower level of the total IgE. Long-term participation in LCF didn't cause any enhanced expression of cellular activation markers in liquidators-86. Specific features of changes in IS depending on a dose of external gamma-irradiation have been established. Increase in the frequency of MN among liquidators, in relation to the number of examinees in each age group, with age has been revealed. Distinctions in the age dynamics of IS in liquidators in the presence and in the absence of MN manifested themselves in a stable level of values of CD3+, CD4+, CD8(+)-T-lymphocytes, immune regulation index, CD95+, serum IgA at the age between 40 and 70 years old with a subsequent reduction in indicators and increase in the content of CD8(+)-T-lymphocytes with age in the absence of MN; continuous increase of CD3-16/56(+)-NK-cells in the presence of MN and decrease in the values after 70 in the absence of MN. Also revealed in IS of the both age groups of liquidators over 70 with and without MN was the deficiency of the T-cell component (CD3+, CD4(+)-T-lymphocytes, CD4+/CD8+ index) and the increase in absolute values of CD8(+)-T-lymphocytes. The growing deficiency of CD4(+)-T-lymphocytes during monitoring against the background of ever rising values of CD8(+)-T-lymphocytes leading to the weakening of the immune regulation due to progressing disorders of the T-lymphocyte regulatory subpopulation distribution can serve an indicator for the adverse prognosis of the life expectancy in the presence of MN.