When the monoclonal antibodies (McAb) were created in the world, it turned a new page of the modern immunology. In the production and the application the McAb is becoming more and more widespread and profound. Some authors at home have used mitogenes to study the radiosensitivity of lymphocyte subsets, but using the monoclonal antibodies as a tool to study the radiation effect of lymphocyte subsets has not been reported in our country. Some authors in foreign countries have preliminarily done this kind of work.,Three kinds of monoclonal antibodies were used in experiments; OKT,4, McAb, OKT,8, McAb and HI,43, McAb to identify T helper (Th) , T suppresser (Ts) and B lymphocytes respectively. After lymphocytes were exposed to 0.1 Gy, 0.25 Gy, 1 Gy and 4 Gy ,60,Co γ-rays immediately, we observed the radiation effect by means of the immunofluorescence tests. 200 cells were counted to obtain the percent of immunofluorescence positive cells. The results indicated that when the Th, Ts and B lymphocytes were irradiated by 0.1 Gy ,60,Co γ-rays, their abilities to combine with McAb decreased significantly. The radiation effect became more and more obvious with increasing radiation dosage. Three kinds of the immunofluorescence positive cells percents were analysed with weighted linear regression methods. The relational coefficients (,r,) of Th, Ts and B lymphocytes were 0.8131, 0.8832 and 0.9086. The significant tests of regression coefficient showed that the radiosensitivities of Ts and B lymphocytes were higher than the Th lymphocytes. The Ts and B lymphocytes had no significant difference.,Lymphocytes are the most radiosensitive cells in an organism. Its membrane is the radiation injury target of cells. There was a report said that when the lymphocytes were exposed to 0.25 Gy radiation, the ultrastructure variation of the cell membrane could be found.,Our experiment showed that when the lymphocyte were exposed to 0.1 Gy ,60,Co γ-rays, the abilities of Th, Ts and B lymphocyte to combine with McAb decreased significantly although the cell's membrane had not been broken.