The complications caused by infection were examined prospectively in the case of 1164 patients who had undergone open heart operation. Postoperative mediastinitis occurred in 15 cases (1.3%). Owing to mediastinal infection verified by bacteriological findings all patients had to undergo surgical intervention. Ten patients were treated by closed mediastinal irrigation. This method was effective in the case of five patients. Granulated sugar treatment was locally applied in five cases because of an infection, relapsing in spite of a closed treatment, and in four cases primarily, because of advanced mediastinitis and sternum osteomyelitis. With the mediastinal cavity being filled with granulated sugar twice a day, a rapid emptying of the wound and granulation tissue formation was observed in all patients. Redressing was easy and painless. Out of the 9 patients treated by granulated sugar three died before being discharged, but none of the deaths were due to wound complications. The rest of the patients were discharged cured averagely after 91.6 +/- 8.0 days. During the average 22 months' follow up period recurrence of sternal infection was not observed in the group treated by granulated sugar, while out of the 5 patients cured by closed mediastinal irrigation two had to undergo another operation after a few months because of the formation of sternal fistula. The authors consider the granulated sugar treatment to be an effective method in the treatment of obstinate and advanced mediastinal infections.