In a prospective randomized study of treatment with radiation therapy (RT) or RT followed by chemotherapy (CT) for patients with Hodgkin's disease stages I-III, four patients developed acute nonlymphocytic leukemia (ANLL) during post-treatment follow-up. There was a significant relationship between the intensity of the treatment and the appearance of this complication: no cases of ANLL were observed among the 128 patients treated with involved field (IF) RT, IF RT followed by CT, total nodal RT alone (TNR), or total lymphoid irradiation alone (TLI) after a follow-up from 21 to 126+ months (median follow-up 76 months). In contrast, four of 36 patients treated with extensive RT followed by CT developed ANLL at 17, 63, 72, and 91 months. Three of these patients had received TLI + CT, the fourth one TNR + CT.