OBJECTIVE To analyze retrospectively the quantity and activation status of the tumor infiltrating cytotoxic lymphocytes in breast cancer and the draining lymph nodes, and its relation to the clinical pathological significance. METHODS Seventy-four breast cancer samples with their corresponding axillary lymph nodes were histologically typed and staged. Cytotxic lymphocytes were analyzed by immunohistochemistry with the monoclonal antibodies against CD8, CD56, granzyme B and perforin. RESULTS The number of infiltrating CD8(+) T cells in the cancerous interstitial tissue were much higher than that in the tumor parenchyma. Compared with the metastatic tumor samples, the CD8(+) T cells were more intensive in the primary tumors (35.7 +/- 16.0 vs. 23.7 +/- 9.6). The tumor infiltrating CD8(+) T cells of patients with 5 years survivals were more than that of the dead cases in this follow-up series death (32.9 +/- 14.1 vs. 20.1 +/- 9.9). There was no significant difference of activated tumor infiltrating cytotoxic T cell analyzed by using the activation marker granzyme B(+) and there was also no significant correlation between the intensity of CD8(+), CD56(+) cells and the clinicopathological stages. However, percentages of the activated cytotoxic lymphocytes in Stage I groups were significantly higher than those in stage III and IV. Moreover, the number of perforin(+) cells was significantly less than that of granzyme B(+) cells, particularly in the cancerous tissue, indicating a dysfunctional status of tumor infiltrating cytotoxic lymphocytes. CONCLUSIONS Activated cytotoxic lymphocytes may play a significant role against the tumor progression and is associated with a favorable prognosis to some extent. However, a putative dysfunctional status of cytotoxic lymphocytes at tumor site may compromise the host immunity against cancer.