A clinical-laboratory survey of 1952 patients with acute feverish diseases developing after tick bite was carried out in the Pre-Ural region of Russia, which is endemic for tick-borne encephalitis and ixodid tick-borne borreliosis, in 1999-2001. Enzyme-linked immunosorbent assay and indirect immunofluorescence assay were used for the detection of tick-borne encephalitis, ixodid tick-borne borreliosis and ehrlichiosis specific antibodies. Tick-borne encephalitis was diagnosed in 22.8% of patients, ixodid tick-borne borreliosis in 50.5%, ehrlichiosis in 4.5% and mixed infections in 2.9%. For the first time in Russia, a new transmitted disease that appeared to be human monocytic ehrlichiosis was identified and its clinical manifestations were described. The common feature of these infections is the acute course and the marked general infectious syndrome at the early period of the disease. Disorders of the nervous system predominate in tick-borne encephalitis. In ixodid tick-borne borreliosis the development of erythema migrans and organic pathology (disorders of the cardio-vascular system and liver) associated with the involvement of the nervous and locomotor system are pathognomonically significant. The specific characteristics of human monocytic ehrlichiosis include nervous impairments, hepatic lesions, the frequent development of a two-wave course and hemogram changes.