Enzyme-linked immunosorbent assay of immunoglobulin G (IgG) activity in cerebrospinal fluid (CSF) and sera was conducted prospectively in 27 patients with tuberculous meningitis (TBM) by using purified protein derivative (PPD) and lipoarabinomannan (LAM) antigens, from January 1989 to August 1990. 29 patients with aseptic meningitis and 49 patients with non-inflammatory neurological illnesses served as controls. All patients had a computed tomography (CT) scan of the head before a lumbar puncture. The IgG antibodies to the antigens were significantly elevated in TBM, and the reactivity was more frequently positive in the CSF than in the sera, suggesting a local synthesis of IgG in the central nervous system (CNS). The sensitivity and the specificity for the diagnosis of TBM were 59.2% and 93.9% for PPD antigen, and 85.2% and 95.9% for LAM antigen, respectively. Assay of IgG reactivity to LAM antigen was clinically very useful for the early diagnosis of TBM and was superior to PPD for detecting the serological evidence of TBM.