Lactic dehydrogenase (LDH) was measured serially in cerebrospinal fluid (CSF) and serum in 23 cases of meningitis (15 pyogenic and 8 tuberculous) and equal number of age and sex matched healthy controls to find out its diagnostic and prognostic significance in cases of meningitis. The LDH activity was significantly elevated in the CSF and serum (p < 0.001) in cases of pyogenic (PM) as well as tuberculous meningitis (TBM). The maximum elevation was seen on the 1st day and the activity declined thereafter. However, in 3 cases of PM and 5 cases of TBM, the LDH activity on subsequent estimations increased serially and all these cases died. Further, the basal LDH activity in the 3 cases of PM who died was significantly higher (p < 0.01) than those who survived. The rise in enzymatic activity in the CSF was significantly higher (p < 0.001) than in the serum in all the cases of meningitis. The LDH activity was significantly higher in PM as compared to TBM (p < 0.001) both in the CSF as well as the serum.