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Intrathecal production of treponemal antibodies was detected in six (25%)patients with early and 44 (28%) with late syphilis who did not show any neurological deficit. Intrathecal production of treponemal antibodies indicating that the CNS was affected led us to suspect asymptomatic neurosyphilis in these patients. Seventeen (1 1 %) patients with late syphilis but no neurosyphilis and only one (4%) with early syphilis showed additional abnormal CSF variables . Surprisingly, six out of 22 patients with treated early and 20 out of 68 patients with treated late syphilis showed evidence of treponemal antibody production within the CNS .We do not know whether these findings indicate that the CNS was affected because of inadequate treatment or merely reflect persistent synthesis of treponemal antibodies associated with cured infection. In one (4%) patient with early and in 21 ( 1 3%)with late syphilis but no neurosyphilis abnormal CSF variables in the absence ofpositive CSF treponemal test results were observed, which excluded syphilitic inflammation of the CNS.

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Serological and non-serological tests were performed in matched samples of cerebrospinal fluid and serum from 236 syphilitic patients. An increased IgG or IgM index, or both, was found about 70 times more often in symptomatic neurosyphilis than in latent syphilis without involvement of the central nervous system. An increased Ig index, together with a cell count greater than 5/microL, was only found in symptomatic neurosyphilis. Although the numbers of data are small, we conclude that the IgG and IgM indexes are valuable tests in the diagnosis of syphilitic involvement of the central nervous system.

Estimates of thromboplastic activity in 1100 samples of cerebrospinal fluid indicate that an increased activity of this clotting factor is a nonspecific indicator of abnormality in the central nervous system, much like (e.g.) an increased count of mononuclear cells and an increased protein content. However, the proportion of abnormal results obtained by these three tests can differ markedly in different neurological disorders. Increased thromboplastic activity is about 14-fold more common in bacterial meningitis than in viral meningitis; thus the thromboplastin determination can be of value in discriminating between bacterial and viral meningitis.