This study compared the sensitivity and specificity of four test systems in detecting Haemophilus influenzae type b, Neisseria meningitidis, Streptococcus pneumoniae, and gram-negative organisms in cerebrospinal fluid (CSF), versus culture. The tests used on CSF from 155 patients with meningitis were the Phadebact coagglutination (CoA) test, the Directigen latex agglutination (LA) test, counterimmunoelectrophoresis (CIE), and the Limulus amebocyte lysate (LAL) test. The sensitivity for patients with bacterial meningitis was 78% (18/23) for LA, 78% (25/32) for CoA, and 67% (18/27) for CIE for detection of H. influenzae type b; 71% (10/14) for CoA, 100% (6/6) for LA, and 50% (6/13) for CIE in detecting S. pneumoniae; and 33% (1/3) for LA and 50% (2/4) for CIE in detecting N. meningitidis. LAL had a sensitivity of 77% (37/48) in detecting CSF gram-negative endotoxin. The specificities of those with bacterial meningitis for H. influenzae, S. pneumoniae, and N. meningitidis tested by LA were, respectively, 100% (35/35), 96% (50/52), and 100% (54/54); for H. influenzae and S. pneumoniae using CoA 97% (62/64) and 96% (80/83); for H. influenzae, S. pneumoniae, and N. meningitidis using CIE 67% (18/27), 50% (6/12), and 50% (2/4). The specificity of LAL was 86% (38/44). The detection of bacterial antigen from CSF in patients with meningitis by commercial agglutination tests is more sensitive than CIE and is highly specific.