Seven cases of acute nonlymphocytic leukemia (ANLL) and one case of a malignant myeloproliferative syndrome have been seen after extensive radiation therapy for non-Hodgkin's lymphoma or chronic lymphocytic leukemia. A myeloproliferative syndrome with abnormalities in granulocytic, erythrocytic, and thrombocytic cell lines was present in all patients and in seven patients preceded ANLL by 2--18 months. The median time to the development of ANLL after primary disease therapy was 61 months (33--98 range). The leukemia was extremely refractory to therapy and median survival after diagnosis of ANLL was two months (range 0--9 months). Leukemia was seen only in those patients who received multiple courses and multiple techniques of radiation therapy.