The most important factors of infection in leukemic patients and immunodepressive effect of chemotherapy are evaluated. The microorganisms causing infections most frequently are considered. The associations of antibiotics for therapy of severe infections are reported. The employement of granulocyte transfusion, in patients with severe neutropenia and infections antibiotico-resistents, is also considered. Dealing with patients liable of infections the possibility of infection prevention and therapy in protected environment is faced. 12 patients affected by acute nonlymphocitic leukemia were treated with cytostatic drugs to induce remission in laminar air flow room. The number of infections is significantly decreased in comparison with of patients treated in open ward. In protected environment it is possible to treat patients with the maximal dose of antiblastic drugs without interruption obtaining higher number of complete remission.