In this study, 460 eligible patients with stage I and II Hodgkin's disease were randomized to treatment with involved field (IF) and extended field (EF) radiotherapy. Lymphangiogram was a requisite of the study. One hundred and seventy-seven patients were staged by laparotomy. The value of EF radiotherapy in improving survival over a 10-year followup was studied. This effect was considered separately for patents staged by laparotomy, for patients staged by lymphangiogram alone, and for patients with and without initial mediastinal involvement. A substantial benefit was seen for the subgroup staged by lymphangiogram alone and without mediastinal disease, with 10-year survival rates of 80% for EF and 56% for IF. For all other groups staged by laparotomy or having mediastinal presentations 10-year survival rates were essentially the same, differing by less than ten percentage points for IF and EF regimens. The advantage of EF treatment in lymphangiogram-staged nonmediastinal disease was realized only when the extended fields included the abdominal para-aortic area.