Due to the improved survival of cancer patients receiving chemo- and radiotherapy, the risk of developing a second primary tumor has become a problem in planning the management of patients with a first malignancy [3]. It has been established that up to 10% of all the acute leukemias are of therapy-induced type, i.e., arise as a consequence of the cytotoxic therapy for a tumor or immunopathological disorder [1]. It is therefore important to quantitate the degree of the carcinogenicity of such compounds, determine the range of patients most at risk of developing a secondary leukemia and outline the measures which should be made in order to minimize the carcinogenicity of various treatment modalities.