We examined the efficacies of the beta-lactam-beta-lactamase inhibitor combinations ampicillin-sulbactam and piperacillin-tazobactam in the treatment of intra-abdominal abscesses caused by a TEM-26-producing strain of Klebsiella pneumoniae. At lower doses, both combinations reduced abscess colony counts by more than 3 log10 CFU/g from that of untreated controls, but treatment with these drugs was inferior to treatment with imipenem. Increasing the doses of the combinations resulted in a further decrease in abscess CFU to a level where both were similar to imipenem in efficacy. These results suggest that the beta-lactam-beta-lactamase inhibitor combinations ampicillin-sulbactam and piperacillin-tazobactam may be viable alternatives for the treatment of serious infections caused by susceptible extended-spectrum beta-lactamase-producing strains of K. pneumoniae.