ABSTRACT
The biologic diagnosis of syphilis is based particularly on the syphilitic serology, as the emphasis of the Treponema pallidum by direct examination is difficult. The serological techniques used are various and contain: TPHA, VDRL, FTAABS. Positive TPHA in the blood indicates the diagnosis of treponematosis, but there is no any serology able to distinguish the syphilis from the other non venereal treponematosis. A positive VDRL may be noticed in non syphilitic cases [false positive serology]. So, it is necessary to ask for two tests [TPHA: treponemic, VDRL: non treponemic]. A correct interpretation of the syphilitic serology permits knowing the various stages of the disease and to follow its evoluation. The decrease of the VDRL quantitive titre is the main criteria of the serologic supervision after treatment. Some difficulties of interpretation are met with cases of neurosyphilis and congenital syphilis. The advent of the new techniques as the ELISA and the PCR make their diagnosis easier but they are still expenxive and difficult to realise