Bacteroides spp., particularly B. fragilis, are well-recognised bacterial pathogens. Production of the typical beta-lactamases of Bacteroides restricts the therapeutic use of beta-lactam agents mainly to the beta-lactamase inhibitor combinations and carbapenems. These compounds have the advantage of broad-spectrum activity and the ability to combat polymicrobial infections. Resistance of Bacteroides spp. to beta-lactam antibiotics appears to be increasing, largely because of an overall increase in beta-lactamase activity. There has been a rise in the prevalence of isolates showing high-level production of typical Bacteroides beta-lactamases and an increase in reports other potent beta-lactamase types. In the case of B. fragilis, metallo-enzymes are a particular threat to current therapeutic practice, as they are not inhibited by common beta-lactamase inhibitors and are able to hydrolyse carbapenems. The presence of permeability barriers may confer low-level beta-lactam resistance and supplement the effect of beta-lactamase activity. There are also sporadic reports of loss of beta-lactam activity because of reduced affinity of the penicillin-binding proteins.