Three beta-lactamase inhibitors in clinical use--clavulanic acid, sulbactam and tazobactam--were investigated for their activity on beta-lactamases from Bacteroides uniformis, Clostridium butyricum and Fusobacterium nucleatum. Purification of the beta-lactamases was carried out by anion-exchange chromatography, gel filtration and FPLC. The inactivation of beta-lactamase activity was determined spectrophotometrically with nitrocefin as substrate. Various concentrations of the inhibitors were preincubated at 30 degrees C together with the enzyme for different periods of time before determination of the beta-lactamase activity. The three beta-lactamases tested were more susceptible to tazobactam than to clavulanic acid and sulbactam. Clavulanic acid and sulbactam reduced the enzyme activity of the Bacteroides uniformis beta-lactamase more effectively than the Clostridium butyricum and Fusobacterium nucleatum beta-lactamases.