Nosocomial meningitis due to gram-negative organisms is a difficult clinical problem to manage because of both antibiotic resistance and poor penetration of many antimicrobials across the blood-brain barrier. Ciprofloxacin has potential in treating this condition when used in high doses. We investigated the plasma and cerebrospinal fluid (CSF) levels of ciprofloxacin in a patient with Pseudomonas aeruginosa meningitis who was treated with 400 mg of intravenous ciprofloxacin every 8 hours. Ciprofloxacin levels in plasma peaked at 10.29 mg/L without resulting in accumulation (8-hour trough levels, <1 mg/L), whereas the CSF level increased to 0.9 mg/L. This CSF level was confirmed to be similar 1 week later. After 1 week of therapy, during which there were no side effects attributable to ciprofloxacin, the organism was eradicated, and there was some clinical improvement. We recommend that 400 mg of intravenous ciprofloxacin every 8 hours be considered for treatment of difficult-to-treat gram-negative bacillary meningitis.