A continuing nationwide susceptibility survey of the Bacteroides fragilis group, begun in 1981, is being conducted at the New England Medical Center. Review of susceptibility testing in years 1986 through 1988 is reported here. Totals of 557 strains in 1986, 506 in 1987, and 534 in 1988 were obtained from seven centers in the United States. The most active beta-lactam drugs were beta-lactamase-inhibitor combinations ticarcillin-clavulanic acid, ampicillin-sulbactam, cefoperazone-sulbactam and the carbapenem imipenem. These drugs had virtually no resistance detected. Their rank order of activity was imipenem, ampicillin-sulbactam, ticarcillin-clavulanic acid, and cefoperazone-sulbactam, all with activity levels greater than cefoxitin or piperacillin, which, in turn, had activity levels greater than moxalactam, ceftizoxime, cefotetan, cefotaxime, cefoperazone, and ceftazidime. No metronidazole- or chloramphenicol-resistant isolates were found. Clindamycin resistance averaged 6% over the 3 years of testing. Ticarcillin-clavulanic acid, ampicillin-sulbactam, imipenem, and the non-beta-lactam drugs displayed uniform excellent activity against the five species of the B. fragilis group tested. The other beta-lactams displayed significant variability of activity among the various species.