A total of 250 cerebrospinal fluid (CSF) specimens were analyzed using a rapid enzyme immunoassay (Pharmacia Meningitis ETA-Test) (EIA) for the detection of antigens of Haemophilus influenzae type b, Neisseria meningitidis (serogroups A, B, C) and Streptococcus pneumoniae (25 selected types). The test is performed in less than 1 h and read by the naked eye. EIA and coagglutination (CoA) were compared with a constructed reference that comprised samples which were either positive by culture and/or on direct microscopy (DM), or in which there were positive results with both EIA and CoA for the bacteria covered by the assays. Using this reference for CSF samples assayed in a period between two meningococcal meningitis epidemics, the sensitivity was 0·86 for EIA and 0·69 for CoA, the specificity 0·95 (EIA) and 0·97 (CoA), the predictive value for a positive result 0·81 (ETA) and 0·87 (CoA) and, the predictive value for a negative result 0·96 (EIA) and 0·93 (CoA). Antibiotics had been given to 54% of the patients before admission. All of the 56 samples that were positive in any of the tests taken during an epidemic of group A meningococcal disease were detected by EIA; CoA was negative in 45% and culture/DM was negative in 32%. Sequential dilutions of two CSF samples from which H. influenzae type b had been isolated, showed the EIA to be 16–32 times more sensitive than CoA. With both technical feasibility and good sensitivity and specificity, the EIA seems to be useful and reliable for the rapid diagnosis of bacterial meningitis, especially in situations where pretreatment with antibiotics are likely.