The essential method in the laboratorydiagnostics of borreliosis (the Lyme disease)is serologic tests indicating the presence of antibodiesfor Borreliaburgdorferi. The value of test resultsdepends not only on specificity and sensitivityof the method used, but also on the patient's individualcharacteristics and on his/her antibodieslevel. In order to avoid false positive and falsenegative serologic tests results, either a highly specific and sensitive ELISA test with appropriatelymatched B. burgdorferi protein fractions as the diagnosticantigen should be wed, or a two-stageexamination is recommended, i.e. positive anddoubtful positive screening test results should beconfirmed by means ofthe Western-blot technique.Due to a limited sensitivity of serologic tests .in some cases, the PCR test may serve as an auxiliarydiagnostic technique. The diagnostic valueof both serologic test and PCR results dependson appropriate selection of clinical material fortest purposes.