This study reports the spread of tumors of mammary gland in dogs. Changes in blood immunological and morphological parameters of affected dogs are presented. Results of immunotherapy used for activation of immune system after surgery showed various level of stimulation. Application of levamisole increase the percentage of T- and B-lymphocytes as well as the ratio of normalized subpopulations of T lymphocytes (T-helper and T-suppressor cells) indicating potential effect of levamisole. Application of BCG improved performance of T- and B-lymphocytes, but in comparison with the effect of levamisole some imbalance between subpopulations of T-helper and T-suppressor cells was detected. In the control group (simple tumor removal) different results were found indicating immunosuppressive effect of tumors.