Lactate levels in the cerebrospinal fluid (CSF) were determined in 21 patients with culture-proved tuberculous meningitis (TBM). All patients showed uniformly high lactate level (greater than or equal to 3.9 mmol/l). Neither the clinical stage of TBM nor the prognosis was related to the CSF lactate concentration. Repeated CSF studies demonstrated persistently high lactate levels in the early stage of illness despite adequate antituberculous therapy.