Approximately 5 - 10 ml of CSF should be collected in two sterile tubes by lumbar or ventricular puncture performed by a physician. In view of the danger of iatrogenic bacterial meningitis, thorough disinfection of the skin is mandatory. Part of the CSF specimen will be used for cytological and chemical examination, and the remainder for the microbiological examination. The specimen should be delivered to the laboratory at once, and processed immediately, since cells disintegrate rapidly. Any delay may produce a cell count that does not reflect the clinical situation of the patient.