A retrospective review of data from two institutions demonstrated that the Limulus amebocyte lysate test was a simple and cost-effective means to screen cerebrospinal fluids (CSF) for Gram-negative agents of meningitis. Results of either gelation Limulus amebocyte lysate (LAL) or chromogenic Limulus amebocyte lysate (CLAL) tests on 1504 CSF were evaluated along with results of antigen detection tests [ADT; either latex agglutination (LA) or counterimmunoelectrophoresis (CIE)], cultures, and Gram-stains. All 127 CSF positive for Haemophilus or Neisseria by culture and/or ADT were also positive by Limulus test (100%). The sensitivities of Gram stain examination, culture, LA, and CIE for these two pathogens were 81%, 91%, 86%, and 63%, respectively. The Limulus test on lumbar CSF was positive in 67% of cases with other Gram-negative bacillary meningitis, in 33% of cases with Gram-negative bacillary abscess or ventriculitis, in none of the cases with Gram-positive, mycobacterial, treponemal, fungal, or viral meningitis, and in 1% of cases with either normal or otherwise negative bacteriologic findings. Overall, sensitivity and specificity of the Limulus test were 97% and 99%, respectively. The cost of either version of the Limulus test was less than 15% of the cost of ADT batteries for Haemophilus and Neisseria. Based on its sensitivity for Haemophilus and Neisseria in CSF, we propose its use as a cost-effective screen to minimize the need for the more expensive ADT batteries.