From 3,404 Ixodes ricinus ticks collected in 12 localities of Styria, Austria in 1990, 15 tick-borne encephalitis (TBE) virus isolates were recovered. Minimal field infection rate reached 4.4 virus containing ticks out of 1,000 collected ticks. Five isolates of TBE virus were obtained from target organs of Apodemus flavicollis trapped in locality Wagnitz. In a serosurvey based on virus neutralizing antibodies high prevalence of TBE virus was demonstrated in A. flavicollis (47.9%) and Clethrionomys glareolus (29.4%). These rodents formed 57.8% and 41.0% of 83 trapped small mammals.