Physiologic compartmentalization effectively isolates the central nervous system from the rest of the body. This isolation not only provides protection of its delicate function from aberrant peripheral influences but also impedes its diagnostic evaluation. Cerebro­ spinal fluid (CSF) bathes the brain and spinal cord, is in dynamic equilibrium with its extracellular fluid, and tends to reflect the state of health and activity of the central nervous system. CSF examination is the most direct and popular method of assessing the central chemical and cellular environment in the living patient or mammal. The purpose of this multidisciplined reference text is to provide the sophisticated knowledge of CSF physiology and pathology necessary for the meaningful interpretation of data obtained by various types of CSF analysis. The methodology for reliable CSF collection, storage, preparation, and analysis is discussed with respect to individual, somatotropic, chronologic, endorcinologic, pharmacologic, and possible artifactual var­ iations in CSF composition. These essential aspects, which ensure the validity of CSF data, are presented to aid the investigator in clinical and experimental protocol formu­ lation and in elimination of possible sources of error.