Acute myeloid leukaemia occurred in six patients who had been treated for Hodgkin's disease for a number of years. Usually the leukaemia diagnosis was preceded by a striking pancytopenic phase, bone-marrow aspiration being more useful diagnostically than biopsy. Five of these six patients have come under observation in the last eighteen months. This extraordinary frequency of secondary acute myeloid leukaemia once again raises the question of the leukaemogenic effect of intensive radiotherapy and chemotherapy, and also new aspects in the therapeutic management of Hodgkin's disease, especially combined radiotherapy and chemotherapy, as well as long-term maintenance chemotherapy.