Epidemic bacterial meningitis in the adult and the elderly are essentially due to Streptococcus pneumoniae. Neisseria meningitidis and Listeria monocytogenes. Their poor prognosis is mainly due to the severity of the associated encephalitis, responsible for neurological sequelae and for mortality ranging from 20 to 30% in pneumonococcal and Listeria meningitis. Treatment associates an antibiotic having rapid antibactericidal action in the CSF, suppression of possible foci of primary infections and intensive care required by the frequency of associated visceral insufficiency. Present research is centered on: 1. the appearance and progression of pneumococcal lines resistant to penicillin; 2. the trials of modulators of the inflammatory response, notably dexamethasone; 3. the improvement of antibiotic concentrations in the CSF and the cerebral parenchyma, particularly in listeria infection.