Concentrations of sulbactam in the CSF of 18 patients with bacterial meningitis who were undergoing treatment with intravenous (iv) ampicillin were determined. Six patients received single doses of sulbactam (1 g) and 12 patients receivedmultiple doses (four times daily) by the iv route at various intervals before lumbar punctures wereperformed to monitor their condition. Concentrations of sulbactam up to 12 µg/ml were detected in the CSF between 1 and 4 hr after dosing, the higher levels being present in the CSF of patients with the most severe meningeal inflammation. There were no significant differences in the concentrations achieved after single or multiple doses of sulbactam, and the concentrations were generally similar to the concurrent concentrations of ampicillin. It is concluded that these results as well as the antibacterial properties of sulbactam plus ampicillin support the evaluation of this combination as an alternative in the treatment of bacterial meningitis.