The penetration of ofloxacin was studied in 22 patients with purulent meningitis or ventriculitis treated with conventional antibiotics. Three successive doses of 200 mg were infused at 12-h intervals during the acute stage of the disease. Ten patients received three additional doses when the meninges were considered to be healed. Cerebrospinal fluid (CSF) was drawn 0.5, 3, 6, or 12 h after the last infusion. Serial plasma and CSF samples were also obtained from patients with ventricular drainage. Concentrations in CSF ranged from 0.96 +/- 0.15 to 1.80 +/- 0.29 microgram/ml, depending on sampling time. The percentage of penetration in ventricular fluid, expressed as the ratio of the CSF area under the curve from 0 to 12 h to the plasma area under the curve from 0 to 12 h, was 73 +/- 6. Ofloxacin readily diffuses into CSF of patients with meningitis or ventriculitis and may be useful for treatment of CSF infections caused by susceptible pathogens.