Tick borreliosis is widespread in the Kirov Province of Russia due to its specific climatic and geographical conditions. Early tick borreliosis was studied in 191 patients in the city of Kirov in 1995-1996. The diagnosis was verified by the epidemiological history, clinical symptoms (chronic erythema migrans), and/or positive serological assays. Tick erythema migrans was detected in 165 (86%) patients. Specific antibodies to Borrelia afcelii antigen were revealed in 128 (67%) patients. The serological tests were false-negative in early infection or just after initiation of treatment. Only 84 (44%) patients with borrelial erythema migrans had specific antibodies to B. afcelii antigen. Mixed tick infection was detected in 6 (3%) patients who showed antibodies to B. afcelii antigen and to tick encephalitis virus. All the patients benefited from wide spectrum antibiotics just within the first days of the disease.