Among the 345 F. tularensis holarctica strains isolated in Europe, Asia and North America, two variants were found: one sensitive and the other resistant to erythromycin, oleandomycin and lincomycin. These characteristics were not associated with virulence, antigenicity, biochemical activity or source of isolation and displayed high stability in passages in laboratory animals or multiple passages in culture media. The two variants are proposed to be designated as biotype (biovar) I, erythromycin sensitive (erys), and biotype (biovar)II, erythromycin resistant (eryR). A predominance of biotype I was observed for western Europe, eastern Siberia and the Far East, as well as North America, whereas biotype II prevailed in central Europe, the European part of USSR, especially the south, and western Siberia. The distribution of biotype II largely coincided with the habitat area of Arvicola terrestris, from which it was isolated with the highest frequency. Within the areas of biotype II prevalence, erythromycin and other macrolide antibiotics, as well as lincomycin should not be used for tularemia therapy.