In the study, we utilized the OKT monoclonal antihuman T lymphocyte antibodies by indirect immunoenzyme staining method to determine T lymphocyte subsets in the peripheral blood of 72 cancer patients treated by local radiotherapy. The haematological assays were performed immediately pre- and postradiotherapy. In the postoperative radiotherapy group (PR group) of 40 breast cancer patients treated by prophylactic postoperative radiotherapy, after radiotherapy blood platelet, white blood cell anti lymphocyt e count decreased significantly. CD₂, CD₄ and CD₈ cell counts all very significantly decreased. Proportion of CD₂ and CD₄ had no apparent change but proportion of CD₈ increased significantly. The group appeared apparent hypoimmunity. While the complete response group (CR group) of 32 cancer patients treated with local radiotherapy, after radiotherapy blood platelet, white blood cell and lymphocyte count had no significant decrease. CD₂, CD₄ and CD₈ cell count had no significant decrease. Proportion of CD₂, CD₄ and CD₈ had no apparent change. The CR group had no apparent hypoimmunity. Comparing decrease rate of immunologic parameters in these two groups, decrease rate of white blood ceil, lymphocyte and T lymphocyte subsets count in CR group significantly were slightened rather than pR group. This study proved that effect of radiation-damaging tumor cell enhance antigenicity of the tumor and stimulate host cell immunity including a type of T-lymphogenesis. Induced hypoimmunity by postoperative radiotherapy should be avoided in this point of view.