200 patients suspected for tick-borne encephalitis (TBE) were examined by the method of the indirect immune rosette-formation test. In 70.15% of patients with the serologically confirmed diagnosis of TBE immune lymphocytes were detected as early as on day 1 of examination. The level of rosette formation was higher in the meningeal form of the disease. Rosette-forming lymphocytes were also detected in 24.06% of patients with the serologically unconfirmed diagnosis of TBE. The test is proposed for the early diagnosis of TBE.