The activity of MK-0826, a new carbapenem, against 309 Bacteroides fragilis group strains was investigated and compared with that of 11 other beta -lactam and 5 non-beta -lactam agents. MK-0826 showed excellent activity (MICs ranged from less than or equal to0.06 to 4 mug/ml). The new carbapenem may be useful in the treatment of mixed anaerobic infections involving B. fragilis group strains.