A simple latex particle agglutination test for the rapid detection of Mycobacterium tuberculosis plasma membrane antigen in cerebrospinal fluid was evaluated in 18 children with tuberculous meningitis and 134 control children with other disorders. The antigen was detected in all 18 patients with tuberculous meningitis, although an initial sample from 1 patient did not contain detectable antigen before it was concentrated. 133 of 134 control samples gave negative results.