Most clinical reports deal with series of patients or single cases under widely different circumstances as to the nature of infection, the duration and mode of chemotherapy, the means of drug concentration assessment, and the expression and interpretation of results. It is generally accepted that the penetration of beta-lactamines, aminoglycosides and vancomycin into the CSF is increased in the presence of infection, and this is confirmed in the results of most animal and human studies. Fluoroquinolones, cotrimoxazole, chloramphenicol, metronidazole, penetrate well into normal meninges. Finally, the reports reviewed above provide data used in predicting the likelihood of attaining adequate CSF levels with any particular antibiotic regimen, for bacterial infection of the CNS. However, the fact that levels can be assessed in the CSF does necessarily mean that drugs are effective in the treatment of the disease. Clinical studies are necessary to provide evidence as to the efficacy of each of the agents in meningitis.