The data on the Borrelia burgdorferi sensu lato prevalence on the taiga tick in Karelia are received. The tick imagoes (733 spm.) are investigated by the PCR method. The prevalence Borrelia on ticks in the Karelia has made 18.3 ± 3.4 %. The most intense situation develops in the Kondopoga region, where high number of ticks is combined with high prevalence of Borrelia.