In some cases, the standard algorithm of clinical and laboratory examination currently used in the Russian Federation does not allow the adequate examination of patients, which hinders both the diagnosis of neurosyphilis and administration of effective therapy. Objective. The objective of this study is to assess the efficacy of used methods of clinical and laboratory diagnostics and optimize establishing adequate diagnosis by testing biosamples obtained from patients with suspected neurosyphilis, using a diagnostic method based on evaluation of the serum/CSF ratio using ITPA index (Intrathecal Treponema pallidum assay), which was not previously used in the Russian Federation. Material and methods. Twenty patients (13 males and 7 females) were examined. Equipment and test systems to determine total immunoglobulin (IgG), total protein in the cerebrospinal fluid, and the number of cells in the cerebrospinal fluid; to perform enzyme immunoassay reactions, microprecipitation, passive hemagglutination, immobilization of Treponema pallidum, immunofluorescence reaction; to count serum/CSF ratio index. Results. The article presents the results of laboratory bioassay (serum and CSF) of patients with suspected neurosyphilis using ITPA-index. We performed a comparative evaluation of diagnostic effectiveness of two methodologies in examination of patients, including the conventional one and the method that was not previously used in Russia. Twenty patients were examined using ITPA-index and high index of serum/CSF ratio was detected in 8 cases, indicating the presence of nervous system involvement. Conclusion. Clinical and laboratory studies of serum/SCF ratio in biosamples from patients with suspected neurosyphilis demonstrated that it is possible to verify the diagnosis in cases of discordant results of conventional laboratory and clinical examination methods.