Examination of ticks for the presence of F. tularensis resulted in the isolation of 29 strains, predominantly from the species D. reticulatus (19x), further from I. ricinus (8x) and from H. concinna (2x). The results confirmed the activity of the known endemic focus in the area of Podunajské Biskupice and revealed three new foci in the localities Smolenice (district of Trnava), Olichov (district of Nitra), and Plást'ovce (district of Levice). In the focus of Podunajské Biskupice the mean infestation of ticks of the species D. reticulatus was around 1.4% over the years of investigation. With regard to the one-year developmental cycle, D. reticulatus can be considered an appropriate indicator of current epizootic activity of the focus, while the occurrence of I. ricinus is rather an indicator of the geographic spread of foci. The third part of the study addresses questions of the ecology of ticks. It analyzes their biological characteristics in our conditions, their spread and bionomy, particularly from aspects related with their epidemiological significance as vectors of Lyma borreliosis and tularemia. Systematic follow up of infestation of ticks with causative agents of borreliosis and tularemia in established endemic foci as well as in epidemiologically indicated localities is an inevitable part of modern surveillance of these infections.