Presence of functional immune system is critical for any attempt aimed at improving survival of breast cancer patients by strategies based on immune system manipulation. We evaluated by flow cytometry the phenotype of peripheral blood leukocyte of 43 breast cancer patients. In 11 patients, the phenotype was evaluated before and during the chemotherapy by combination of doxorubicin and paclitaxel (AT). Compared with controls breast cancer patients had significantly higher relative and absolute numbers of CD3 HLA-DR+, CD3+CD69+ and CD14+CD16+, and significantly lower percentages of CD3 and CD8+CD28+ cells. After one cycle of AT, the absolute numbers of CD3 , CD3+CD4+, CD3+CD8+ and CD8+CD28+ cells increased significantly. Present data show a presence of T-cell activation in breast cancer patients. Administration of AT may lead to an increase in functional T-cells in peripheral blood, indicating a potential for combining chemotherapy with immunotherapy in the treatment of breast cancer patients.