Serological tests for detection of borrelial antibodies are frequently used in laboratory diagnostics of Lyme borreliosis. Unfortunately these tests are not standardized and the results obtained with different assays may not be concordant. The aim of the present study was to compare two different serological tests, IFA and LIAISON, for detection of Borrelia burgdorferi sensu lato IgM and IgG antibody. We analyzed the serological immune response in 383 patients with different clinical manifestations of Lyme borreliosis and in 49 healthy blood donors. LIAISON detected IgM and IgG antibodies more often than IFA in all groups of patients except those with chronic Lyme borreliosis. The differences were significant for IgM and IgG antibodies in patients with solitary erythema migrans and in those with early disseminated Lyme borreliosis. There was no significant difference in the specificity of the two tests.