To reveal clinical signs and symptoms of Lyme's disease in the population of the endemic area, clinical and serological examinations of 416 persons have been performed. Preliminary screening, using indirect immunofluorescence, has revealed in 230 persons (group I) antibodies to the agent of the disease at a titre of greater than or equal to 1:20. Group II consisted of 186 patients who had not been serologically examined. Lyme's disease diagnosed in most cases by erythema annulare was found in 8 patients from group I and 12 patients from group II, all in all in 20 patients (4.8%) of all the patients examined. No typical late signs and symptoms of Lyme's disease have been observed. High antibody titres (greater than or equal to 1:80) were found in 24% of patients in group I and in 4.1% of patients in group II. Different clinical and immunological courses of borreliosis in the endemic area are discussed.