The in-vitro activity of ticarcillin alone and with 4 and 8 mg/l of clavulanic acid, has been studied on 100 strains of Bacteroides (66 Bacteroides fragilis, 13 B. ovatus, 11 B. vulgatus, 6 B. distasonis, 4 B. thetaiotaomicron) by an agar-dilution method and compared to that of latamoxef cefoxitin, cefotaxime, ceftizoxime, ceftriaxone, cefmenoxime, ceftazidime and metronidazole. All the strains tested were susceptible to the combination of ticarcillin-clavulanic acid (MIC less than or equal to 8 mg/l), to metronidazole (MIC less than or equal to 4 mg/l), and to cefoxitin (MIC less than or equal to 32 mg/l). The combination of ticarcillin and clavulanic acid has an activity superior to that of ticarcillin alone. The MIC90 was 32 mg/l for ticarcillin alone, 1 and 0.5 mg/l for ticarcillin combined with 4 and 8 mg/l of clavulanic acid respectively. Against all the tested strains, cefoxitin was the most active of the cephalosporins, followed by latamoxef (3% of all strains with an MIC greater than 32 mg/l), cefotaxime (5%), ceftizoxime (9%), ceftriaxone (13%), cefmenoxime (17%) and ceftazidime (33%). Differences in sensitivity to cephalosporins were observed within species; the B. ovatus was clearly more resistant than B. fragilis and B. vulgatus. In all species, the combination of ticarcillin and clavulanic acid was always highly active, with MICs less than or equal to 0.01-8 mg/l.