The research of clinical characteristics of different tick mixed infections etiological variants in children — tick-borne encephalitis, ixodid tick-borne borreliosis, granulocytic anaplasmosis and monocytic ehrlichiosis in human in Kemerovo region showed a possibility of feverish meningeal and meningoencephalitic forms of disease. The comparative analysis of mono- and mixed infections according to the principal clinical criteria showed the predominance of non-specific symptoms and more severe clinical course in mixed etiology, the pathognomonic for ixodid tick-borne borreliosis symptoms are rare. One of the main causes of severity of state and sequences of the disease is the autotoxemia syndrome. The use of the luciferase method in the diagnosing of the autotoxemia syndrome in tick mixed infections allows to predict the development of severe forms of the disease.