A modified latex agglutination test was designed and evaluated for the rapid detection of Streptococcus pneumoniae and haemophilus influenzae type b capsular antigens, and for direct serotyping of Streptococcus pneumoniae in the cerebrospinal fluid. Reagents were prepared by sensitizing latex particles with Omniserum (against 83 capsular serotypes of pneumococci) and Haemophilus influenzae type b burro antiserum. For serotyping reagents, latex particles were similarly coated with nine pneumococcal pool (a to I) antisera and 46 individual pneumococcal serogroup/serotype specific antisera. The test was performed on cerebrospinal fluid from 298 patients with suspected meningitis. Serotyping was done directly on untreated cerebrospinal fluid samples showing positive reactions with the Omniserum reagent. Pneumococcal or Haemophilus influenzae type b antigens were detected in 41 patients; in 32 of these the etiology was established by culture and in 2 by smear examination. Five of the remaining seven cases were judged clinically and by cytological examination of cerebrospinal fluid to have partially treated bacterial meningitis. In two cases the test was false positive. The overall sensitivity and specificity of the latex agglutination test for the detection of Streptococcus pneumoniae and Haemophilus influenzae type b antigens was 100% and 96.8% respectively. The commonest pneumococcal serotypes were type 1 (30%), types 6 and 19 (10% each). The latex agglutination test is rapid and simple to perform, yielding serotype data directly by testing of cerebrospinal fluid.