The objective of the work to introduce screening PCR into the diagnosis of Borrelia burgdorferi sensu lato in the vector selection of the most suitable primer, derived from chromosomal DNA and detection of different genome species. The sensitivity of primers, described in the literature (LD, 16S, Wk, 5S-23S) was tested by different amounts of DNA strains of borrelias. The most sensitive primer--LD was used for detection of borrelias in the vector. Ticks were collected in municipal parks from 1995-1997. A total of 635 ticks were examined. The positivity of the group differs in individual years: 9.2% in 1995, 3.4% in 1996, and 4.5% in 1997. Adult ticks were markedly more infected than nymphs. Borrelia garinii prevails at the site, Borrelia burgdorferi sensu stricto was not detected so far. Mixed infection with Borrelia garinii/Borrelia afzelii was found in 1997 in one sample (female ticks). PCR is a sensitive and specific method suitable for assessment of the herd immunity of ticks with borrelias. It makes it possible to differentiate with a relatively high sensitivity individual genome species of Borrelia burgdorferi in the vector. Before its use the sensitivity of the reaction must be tested in the presence of tick DNA.