Many researchers and clinicians have been concerned about the potential impact of anesthetic agents on human immune system. There have been expanding evidences associating an- esthesia and surgery with down-regulation of immune functions. Immune alterations associated with anesthesia and surgery are manifested by lymphapenia and granulocytosis, decreased T cell and B cell counts, decreased delayed hypersensitivity responses, increased metastatic rates of tumors, depressed basal natural killer cell activity and enhanced antibody responses. All of the above effects have been described as short lived, returning to normal levels within 3 -7 days following surgery. But the clinical significance of suppressed immunity in the perioperative period is important, it has been suggested that such suppression contributes to postoperative dissemination of carcinoma and to postoperative infections. The present study was designed to examine the effects of general and epidural anesthesia on the lymphocyte subpopulations in patients undergoing hysterectomy. Halothane was used as a main anesthetic agent in general anesthesia group(10 patients) while bupivacaine was used in epidural anesthesia group(10 patients). Lymphocyte, granulocytes and T-lymphocyte subpopulations were counted before, during and after anesthesia. A significant reduction in peripheral total T-lymphocyte to total lymphocyte ratio(CD3+ percentage), Helper/Inducer T-lymphocyte to total T-lymphocyte ratio(CD4+ percentage), Suppressor/Cytotoxic T-lymphocyte to total T- lymphocyte ratio(CD8+ percentage) and Suppressor/Inducer T-1ymphocyte to total T-lympho- cyte ratio(CD4+ and CD45R+ percentage) was seen in patients under general anesthesia but minimal changes were found in the patients who had an epidural anesthesia. The results suggest that the immunosuppressive alterations in lymphocyte subsets induced by surgery and general anesthesia can be prevented to certain degree by epidural anesthesia.