This study reports 35 cases of posttherapeutic acute leukemia and reviews the literature on this subject. These AL's are characterized by a high incidence of anemia, in particular refractory anemia, preceding the hematological disorder by several months, by the frequent finding of myelofibrosis, by the essentially granulocytic nature of the AL, and by the low rate of remission and the, in general, extremely short sruvival of a few months. These leukemias may develop following continuous chemotherapy with an alkylating agent, radiotherapy of various extent, or most commonly following intensive treatment with extensive irradiation and polychemotherapy as in the management of Hodgkin's disease. In view of these therapeutic hazards, the present objectives are the modification of alkylating agent therapy by the use of other drugs and sequential administration, and a reduction in the dose and field of irradiation and the duration of polychemotherapy, as in Hodgkin's disease; all present protocols are orientated in this direction.