94 patients with Hodgkin's disease PS I or II, treated during the period 1969-78 and followed until death, or from 33 to 136 months after initiation of therapy, were analysed. 47 patients had been treated with radiotherapy alone (mantle field irradiation and, in all but 12 cases, irradiation of infradiaphragmatic lymph nodes), while the other 47 had been treated with mantle field irradiation plus 6 cycles of combination chemotherapy (MOPP or an equivalent regimen). Of the patients treated with radiotherapy alone, 13 relapsed whereas only 1 of the patients treated with radiotherapy plus combination chemotherapy relapsed. The initial tumour burden of each patient was estimated, combining tumour size of each involved area and number of sites involved. For patients treated with radiotherapy alone, a large tumour burden singled out the patients destined to relapse more accurately than other prognostic factors including pathological stage, B-symptoms, mediastinal involvement, bulky mediastinal involvement, and number of sites involved.