The high medical and social significance of syphilis still determines the urgency of the problem of the effectiveness of its laboratory diagnostics and the availability of domestic highly effective confirmatory tests, especially necessary for the study of samples, in the assessment of which screening tests give ambiguous results. In the practice of laboratory tests for syphilis, a special role is given to confirmatory tests, in particular, immune blotting (IB), which allows to detect antibodies to individual Treponema pallidum antigens in the test sample. Purpose — to evaluate the effectiveness of linear immunoblotting (LIB) in confirmatory studies of serum samples obtained from patients with suspected syphilis. Material and methods. 54 samples of blood serum were studied, during the preliminary study of which by the methods of microprecipitation reaction and passive hemagglutination reaction, enzyme immunoassay, ambiguous results were obtained. The LIB was performed using the Line-Blot-syphilis test system (CJSC EKOlab). Results. Among 54 samples with uncertain results of preliminary studies for the presence of antibodies to T.pallidum, neither IgM nor IgG were detected by LIB in 29 samples; specific IgG and/or IgM were detected in 21 samples. Conclusion. High diagnostic effectiveness of the used test system is demonstrated.