A lymphocyte chromosome analysis of short-term cultured whole peripheral blood of 14 nurses in the radiotherapy/oncology ward of the radiological clinic (working in health risk conditions for an average of 14 years) classified them into a high risk genetic group. They were found to have 4.7% cells with chromosomal aberrations as compared with 1.5% such cells in the control group. The said difference had a high statistical significance (p<0.001). Only aberrations of the structural type were evaluated.The mitotic activity of peripheral blood lymphocytes in the study group was also adversely affected (MI=1.8) compared with the control group (MI=2.9). Cytogenetic peripheral lymphocyte analysis used as a collective biological exposure test is being considered for incorporation in the system of preventive medical chec-kups of nurses working in radiotherapy/oncology wards.