We evaluated immunofluorescence techniques to investigate the presence of S pneumoniae, N meningitidis, H influenzae types a and b and L monocytogenes in 85 samples of CSF fluid: 60 were taken from patients suffering meningitis and 25 from a control group. Results were compared to conventional bacteriologic methods. There were no false positive results in the control group. In patients with meningitis, 28 were positive by both methods. Nine additional patients were positive only to immunofluorescence which allowed identification of S pneumoniae in 6, N meningitidis in 2 and H influenzae in 1. 37 samples were positive by immunofluorescence and 28 of them were positive to conventional bacteriology. There was only 1 case of Group B streptococcus identified by bacteriology which was not diagnosed by immunofluorescence. Thus, immunofluorescence increases the ability to make a bacteriologic diagnosis in patients with meningitis.