Infections of the CNS have a high mortality, and rapid laboratory diagnosis and adequate antimicrobial therapy are critically important for their management. New techniques assist the clinical microbiology laboratory to isolate and identify micro-organisms more rapidly and accurately than with the use of classic procedures. Microbial identification using immunologic and DNA hybridization techniques has importantly reduced the time needed for the diagnosis of infectious diseases. Culture, however, is still the standard method to confirm the identity of an organism isolated from CSF or CNS sites. With the increase in the number of antimicrobial agents and the recognition of resistance in many isolates, antimicrobial susceptibility testing has become extremely important in the selection of optimal antimicrobial therapy. Communication between the physician and the clinical microbiology laboratory is essential for optimum patient care.