This review deals with the differences between leukemias--induced by alkylating agents as opposed to a "new form" of treatment related leukemia due to prior exposure to epipodophyllotoxins the latter having a short treatment--disease onset interval, absence of a MDS phase, a monocytic component and cytogenetic abnormalities involving the 11q23 band. The link between the existence of oncogenes or tumor suppressor genes located on the involved portion of chromosome 11 and the development of epipodophyllotoxin-related leukemia still needs to be examined. Alkylating agents--induced leukemias have a longer treatment--disease onset interval, have a prior myelodysplastic syndrome, and are most frequent myeloblastic or myelomonocytic in nature. Karyotype analysis reveals partial or complete deletion of chromosomes no. 5 or 7. This form of leukemia is highly resistant to treatment in the majority of cases. Some of the possible molecular mechanisms of leukemogenesis are discussed.