Gamma glutamyl transpeptidase (GGTP) was measured serially in cerebrospinal fluid (CSF) and serum in 23 cases of meningitis (15 pyogenic and 8 tuberculous meningitis) and an equal number of age and sex matched healthy controls, to find out its diagnostic and prognostic significance in meningitis. GGTP activity was significantly elevated (p less than 0.001) in CSF and serum in meningitis as compared to control subjects. Levels were significantly higher in pyogenic as compared to tuberculous meningitis (p less than 0.001) and in CSF than in serum (p less than 0.001). The maximum elevation was seen on the 1st day and thereafter the activity declined in the majority (65.2%) of cases. However, in 3 cases of pyogenic meningitis and 5 cases of tuberculous meningitis, the GGTP activity on subsequent estimation increased serially; all these 8 cases died. It is concluded that CSF GGTP activity is significantly elevated in meningitis and serial rise in its activity is associated with poor prognosis and even fatal outcome.