Relapse rates of 75 patients with previously untreated Hodgkin's disease with stages I and II nodular sclerosis were analyzed according to the mediastinal involvement. The overall relapse rate was 22.6%. The probability of relapse was much greater for patients with large mediastinal involvement (66.6%) compared with 17% for patients with small mass, and 11.7% of patients without mediastinal involvement (P less than 0.001). There was no significant difference in recurrence rates between patients without mediastinal mass and patients with a small mass, and in these patients adjuvant chemotherapy MOPP after radiotherapy showed an evident benefit in reducing the relapse rate. On the other hand, no beneficial effect of adjuvant chemotherapy was observed in patients with large mediastinal involvement. Finally, in the 17 relapsing patients, 'salvage' chemotherapy was less effective in patients with large mediastinal mass than in those with small or no mediastinal involvement.