Résumé : Oligonucleotide primers were used in the polymerase chain reaction assay to amplify specific DNA regions of the Borrelia burgdorferi 49-kb linear plasmid. One set of primers identifies a 442-bp DNA fragment in the OspA gene and a second pair of amplimers, a 176-bp DNA piece located in the OspB gene. The last set of primers, OspBpc3/pc4, outperformed the other pair in discriminating pathogenic North American or European isolates from related bacterial species, detected down to 4 spirochaetes, and was suitable for the identification of B. burgdorferi in biological samples, such as synovial and cerebrospinal fluids.