At present time the most rapid and cheap way for ionizing susceptibility estimation is to analyse the human cells sensitivity to test-irradiation ex vivo. The peripheral blood lymphocytes are most often used for these purposes. These cells can be very easily be collected for an analysis and could be a good reflection for whole human body sensitivity to IR due to their high radiosensitivity. Complex investigations can give an appropriate results in the ex vivo test-irradiated cells using a combination such parameters as the free radicals production rate, the activity of key antioxidant enzymes as the superoxide anion dismutase, the DNA damages and their repair, the cytogenetic disturbances, and the cell death frequency. The results of estimation of people with abnormal radiosensitivity among pilots and prostate cancer patients are presented in the paper as an example of practical application of such phenomenological biomarkers in medicine. As criteria for individual radiosensitivity estimation using test-irradiation of blood lymphocytes ex vivo we chose: DNA double-strand breaks (DSB) induction; capacity of DNA SSB repair system; apoptotic cell death frequency. Our results show that criteria used in the study allow to make judgment about the state of blood lymphocytes in individuals. An analysis of cellular response to test-irradiation ex vivo can be recommended for identification of people with an increased sensibility to ionizing irradiation.