During 1997–1999 607 sera were obtained from subjects immunized with vaccine FSME-Immun. The presence of antibodies was assessed using EIA TBEV-Ig TEST-Line tests, Clinical Diagnostics, Immunozym FSME of Immuno Co. and the virus neutralizing test. Between the results of tests sufficient correlation was not found to allow valid evaluation of the presence of postvaccination antibodies by several methods. When using the Immunozyme FSME test it was found that on the day of administration of the 4 th dose of vaccine 15 subjects of 94 had an antibody titre equal to or < 126 VIEU/ml, on the day of administration of the 5 th dose this was the case in 5 of 13 immunized subjects. After administration of the 3 rd , 4 th and 5 th dose adequate, i.e. at least three-year immunity, was acquired, depending on age, by 64.1–97.9% of the immunized subjects. As antibody titres higher than 600 VIEU/ml in different age groups were recorded only in 20.0–61.7% of the subjects, the authors do not consider it desirable in subjects immunized with the Austrian vaccine to prolong the time interval between vaccinations beyond three years.

        Key words: tick-borne encephalitis – vaccination – immunogenicity.