47 patients with advanced Hodgkin's disease (stage IIIB or IV) and mediastinal involvement, treated during the period 1969-78 and followed till death or from 36 to 126 months after initiation of therapy, were analysed. All 47 patients had received combination chemotherapy (MOPP or equivalent regimens). 20 had also received additional radiotherapy to mediastinum (and in some cases to other involved areas as well). The 2 treatment groups did not differ significantly with regard to the more important prognostic factors. Both in the case of stages IV and IIIB patients in the group treated with combination chemotherapy alone, remissions were significantly more often only partial, the frequency of relapse and of treatment failure was significantly higher, and relapse-free survival was significantly poorer than in the group treated with additional radiotherapy. Furthermore, survival from Hodgkin's disease and crude survival including all causes of death were significantly better for patients treated with combination chemotherapy plus mediastinal irradiation. Consequently, for patients with advanced Hodgkin's disease and mediastinal involvement a combined approach including radiotherapy as well as combination chemotherapy would seem advisable.