Leukemic cells are highly sensitive to chemotherapeutic agents. A reduction of the leukemic burden is easily achieved by chemotherapy in most cases. However, it is difficult to reduce the number of leukemic cells to such an extent that a regrowth does not occur and the patient is cured. Traditionally the therapy of acute leukemia is divided into induction and post remission therapy. The aim of the induction therapy is to reduce the number of leukemic cells to a morphologically undetectable level allowing normal hemopoiesis to recover. The goal of the post remission treatment is a further reduction of leukemic cells to zero or to very low levels which can be controlled by (still unknown) endogenous mechanisms. In some recent treatment protocols induction and the early part of post remission treatment are not strictly separated.