The mosquitoes were caught within the period of their highest activity, i.e. June August 2001, in recreational areas of the city of Szczecin. Spirochetes, Borrelia burgdorferi sensu lato were detected in mosquitoes with the aid of the method of indirect immunofluorescence (IFA) using rabbit anti-Borrelia burgdorferi antibodies and goat anti-rabbit IgG marked with fluorescein isothiocyanate (FITC). A total of 639 mosquito females representing genera Aedes (99.1%) and Culex (0.9%) were collected. The mean value of the infection rate of mosquitoes from the area studied was 1.25%. The highest infection rate was recorded in June (3.2%), while the lowest - in July (0.6%). All mosquitoes infected with Borrelia burgdorferi spirochetes belonged to the genus Aedes. The results of the present study confirm a potential role of those arthropods in epidemiology of Lyme borreliosis.