In 38 breast cancer patients were examined the following immune system parameters: total and active T lymphocytes; killer cells; bastogenic response to Phytohaemaglutinin; leucocyte migration inhibition test with autologous tumor extract; serum immunoglobulins and phagocytosis and intracellular killing of Candida albicans. The immunological evaluations were made in pre-surgery and after each 3 months, during 18 months. In stage I practically there was no difference with controls. The active T lymphocytes were significant decreased until 15 months post surgery in stage II and in all samples stages III and IV. The response to Phytohaemaglutinin was diminished in all samples of stages II, III and IV. A recognition and sensitiveness to tumoral antigen were observed until 6 months post surgery in stage I and during checking time in the others stages. Respect to the phagocytic function only the intracellular killing mechanism failed at 3 months post surgery.