Abstract     Problem statement : Lactate dehydrogenise is and important intracellular enzyme which acts as catalyst in oxidation reduction intracellular enzyme which acts as catalyst in oxidation reduction of living organisms, The CSF is situated in subarachnoid space lying between arachnoids and parameter. The CSF is produced by active transport of Na⁺ across the choroids plexus, from the vascular compartment to the cerebral ventricles. The observations made were as follows: The maximum prevalence of different types of meningitis was in the age group 0 to 10 years of age. The LDH level did rise quite significantly in pyogenic meningitis. It was almost concluded that the estimation of CSF-LDH is diagnostic. In case of tuberculosis meningitis also the CSF –LDH level was significantly high but less than of pyogenic meningitis. In viral meningitis the CSF –LDH level was slightly higher than that of normal and significantly lower than that of tuberculosis meningitis and pyogenic meningitis. Methods: In ongoing study twenty apparently healthy subjects and sixty patients suffering from meningitis due to different aetiology are selected for estimation of LDH activity in CSF. They year aged 5- 65 Years in between. All patients were admitted in the indoors of medicine and Paediatrics, Department of M.G.M. Medical College and L.S.K. Hospital Kishanganj, Bihar. Results: In the present series the cases of study group included those of clear cut diagnosis. The cases with ambiguous cytology and chemistry were excluded, so that the conclusion on LDH level assay may be sharp and precise. Biochemical parameters of CSF fluid – Sugar, Protein, and LDH - value were compared both case and control group and statistical analysis were calculated by the help of SPSS software. Conclusion: CSF-LDH estimation is of importance as a diagnostic and prognostic tool as far as the dreaded disease of different type of meningitis are concerned.