A group of 180 patients with diagnosed Lyme borreliosis were examined for the presence of infection with Borrelia burgdorferi sensu lato (B. burgdorferi s.l.) by serologic tests with B. burgdorferi s.l. antigens (IgM-ELISA, IgG-ELISA, IgM-immunoblot, IgG-immunoblot) and by polymerase chain reaction (PCR, nested-PCR) for detection of B. burgdorferi s.l. DNA in peripheral blood. A total of 61.7%, 53.9%, 62.2%, and 59.4% of the examined patients' sera showed positive or borderline results in the serologic tests IgM-ELISA, IgG-ELISA, IgM-immunoblot, and IgG immunoblot, respectively. The results of the tests IgM-ELISA and IgM-immunoblot were significantly correlated (p<0.001). A higher degree of the correlation (p<0.000001) was found at the comparison of results obtained with IgG-ELISA and IgG-immunoblot. The correlation between the positive findings in the IgM-ELISA and detection with IgM-immunoblot the diagnostically important B. burgdorferi s.l. OspC surface protein was relatively low but statistically significant (0.01B. burgdorferi s.l. antigen, the VlsE protein (p<0.000001). The presence of B. burgdorferi s.l. DNA was found by PCR in 20 out 180 examined blood samples (11.1%). No correlation was found to exist between the PCR results and the results of any of the serologic tests for detection of anti B. burgdorferi s.l. antibodies of IgM class. PCR results correlated significantly at a relatively low level (0.01<p<0.05) with the results of IgG-ELISA, but not with the results of IgG-immunoblot with regard to total reactions (0.2<p<0.1). By contrast, a distinctly significant correlation was found between the PCR results and detection of the VlsE protein with IgG-immunoblot (0.001<p<0.01). In conclusion, the results of the present study suggest that antibodies of IgG class are the most reliable marker in laboratory diagnostics of Lyme borreliosis, in particular those directed against VlsE surface protein of Borrelia burgdorferi sensu lato.