The results of this study show that there is a high frequency of resistant species in the Bacteroides fragilis group in the intestinal tract of children and adults in Brazil. B. fragilis was not studied. Of the 73 strains examined, B. distasonis was the most resistant species to penicillin, cefoxitin, cefotaxime and clindamycin. High rates of multiresistance were found, most commonly to penicillin and clindamycin (18 of 36 strains). High levels of beta-lactamase production were detected in isolates showing high resistance to penicillin and multiresistance to the cephamycins, suggesting a widespread dissemination of such resistance.