Fifty samples of cerebrospinal fluid (CSF) from patients with acute bacterial meningitis were studied with direct gram examination, culture and latex agglutination. Twenty one of these samples had previous antimicrobial treatment. In 42 patients, blood cultures were also made. Thirty control CSF samples were also studied. The diagnostic yield of CSF culture was 72%, of direct gram examination 74% and latex agglutination 80%. All the techniques as a whole has a diagnostic yield of 92%. In the 21 CSF samples with previous antimicrobial treatment, culture was positive in 47.6% and latex agglutination in 85.7%. All control CSF samples were negative. It is concluded that the diagnostic yield of latex agglutination test in patients with previous antimicrobial treatment is significantly better than culture.