Fifteen cases of mediastinitis developing after 1,164 open-heart operations (incidence 1.3%) were analyzed. Closed mediastinal irrigation was used as primary therapy in ten cases and led to complete healing in five. Granulated sugar treatment was given primarily to four patients and to five others after failure of closed mediastinal irrigation. The sugar treatment was successful in six patients with hospital stay averaging 91.6 +/- 8 days. The three other patients in this group died before discharge from hospital. During 22-month follow-up there was no recurrence of mediastinitis in the granulated sugar group, but reoperation was necessitated by sternal fistula in two of the patients with closed mediastinal irrigation. Granulated sugar treatment is effective in refractory, severe mediastinal infections.