1. Six cases of leukemia occurring in patients exposed to varying doses of x-ray are reported in this article.
2. The difficulties in evaluating the dosage of radiation is well illustrated in most of these cases.
3. Latent periods were variable and difficult to estimate accurately. It is pointed out that the latent periods in radiation-induced leukemia usually are from three to 10 years in length.
4. All cases in this group were acute leukemias; in four the onset simulated aplastic anemia and diagnosis was verified only after bone marrow aspiration or biopsy.
5. The difficulties in establishing criteria for the diagnosis of radiation-induced leukemia in the present inadequate state of our knowledge are pointed out. In all cases of leukemia attributed to ionizing irradiation it is urgently necessary to publish all information in as complete detail as possible.