We used a test based on the polymerase chain reaction (PCR) for the detection of Mycobacterium tuberculosis DNA in 11 CSF samples from 10 HIV-seropositive patients in whom tuberculous meningitis was suspected. PCR was positive in nine samples from eight patients in whom clinical data, CSF findings, evidence of tuberculosis at an extraneural site, and response to antituberculous drug therapy supported the diagnosis, whereas cultures were positive in five of these nine samples and staining in only one. The PCR was negative in 14 CSF samples from the control group.