The dynamic changes of the T cell subsets in the peripheral blood and the serum level of immunoglobin and complement C3 were observed in 32 breast cancer patients before and after surgery and after radiotherapy.20 patients with benign breast diseases and 20 normal women were observed likewise.It was found that the Ts cells and serum IgG and IgA were significantly increased and the TH/Ts ratio markedly decreased in the breast cancer group as compared with those of other 2 groups.In the first postoperative week,TH cells and TH/TS ratio were markedly decreased in all cases operated on.One month after operation,all the parameters returned nearly to the normal level in the group with benign breast diseases.In the group without radiotherapy,the proportion of OKT3+ cells in the 3rd postoperative month and OKT4+ cells in the 6th postoperative month exceeded the preoperative level while that of OKT8+ cells decreased.In the first week after radiotherapy,TH cells decreased,Ts cells increased and TH/Ts ratio decreased significantly.Meanwhile serum IgG was elevated.OKT3+ cells markedly increased in the 6th month after radiotherapy and OKT8+ cells decreased 1 year after that.The immunore-active state of breast cancer patients and the effects of therapeutic measures on them were discussed.