Thymosin α 1 (Tα 1) is a biologically active polypeptide purified from TF5 and has been completely characterized .It is an acidic peptide with an isoelectric point of 4.2 and a molecular weight of 3108.Tα 1 is considered as an importent biological response modifier which amplifies T-cell immunity. Included in its immunomodulatory properties is the ability to enhance the production of IL-2 and expression of the IL-2 receptor in mitogen- stimulated T-cells.Tα 1 also stimulates the differentiation and maturation of T lympocytes ,auguments the ratio of pro-T cells and strengthens the function of Th cells, so that the function of immune system can be significantly amplified.Additionally , Tα 1 can antagonize dexamethasone-induced apoptosis of subpopulations of thymocytes.In clinical trials, thymic hormones strengthen the effects of immnomodulators in immunodeficiencies ,autoimmune diseases,and neoplastic malignancies. Combined chemoimmunotherapeutical anti-cancer treatment seems to be more efficacious than chemotherapy alone , and the marked hematopoietic toxicity associated with most chemotherapeutical clinical trials can be reduced significantly by the addition of immunotherapy. Thymosin α 1 (Tα 1) is a biologically active polypeptide purified from TF5 and has been characterized characterized. It is an acidic peptide with an isoelectric point of 4.2 and a molecular weight of 3108. Tα 1 is considered as an importent biological response modifier which Included in its immunomodulatory properties is the ability to enhance the production of IL-2 and expression of the IL-2 receptor in mitogen-stimulated T-cells. Tα 1 also stimulates the differentiation and maturation of T lymphocytes, auguments the ratio of pro-T cells and strengthens the function of Th cells, so that the function of immune system can be significantly amplified. Additionally, Tα 1 can antagonize dexamethasone-induced apoptosis of subpopulations of thymocytes. clinical trials, thymic hormones strengthen the effects of immnomodulators in immunodeficiencies, autoimmune diseases, and neoplastic malignancies. Combined chemoimmunotherapeutical anti-cancer treatment to be more efficacious than chemotherapy alone, and the marked hematopoietic toxicity associated with most chemotherapeutical clinical trials can be reduced significantly by the addition of immunotherapy.