DNAs from various Borrelia associated with Lyme disease were reciprocally hybridized. This genomic taxonomy method showed that Lyme disease agent comprised three genomic species. Two species could be differentiated by phenotypic characters as major proteins molecular weights and monoclonal antibodies reactivity. Western-blot with sera from patients suffering from different clinical forms of Lyme disease: arthritis, meningoradiculitis and Acrodermatitis Chronicum Atrophicans showed that each of these evolutive forms was preferentially associated with one of the species, respectively: Borrelia burgdorferi sensu stricto, Borrelia garinii and Borrelia group VS 461. Furthermore, geographical repartition of these three species was heterogeneous. B. burgdorferi sensu stricto seems to be the only one present in the United States of America, whereas it coexists in Europe mainly with B. garinii in Western Europe and Borrelia group VS 461 in Northern Europe.