Acute nonlymphocytic leukaemia developed in seven patients treated for Hodgkin's disease. All had received intensive radiotherapy and chemotherapy. One patient had clinical evidence of active Hodgkin's disease at the time of diagnosis of acute leukaemia, and of four other patients who had a post mortem examination another showed evidence of Hodgkin's disease. The median time from the first presentation with Hodgkin's disease to the development of acute leukaemia was 7.7 years. Chromosomal abnormalities were found in four patients. A preleukaemic phase was present in three patients. Survival following diagnosis of acute leukaemia was short (median four weeks) and only one patient achieved a complete remission. Although published data suggests that radiation exposure is an important aetiologic factor in the induction of acute leukaemia in patients with Hodgkin's disease, it appears likely that additional chemotherapy may have a significant potentiating effect.