Indirect immunofluorescence, ELISA and immunoblot test systems for the detection of antibodies against tick-borne encephalitis (TBE) virus were developed and evaluated. Sera from 112 patients with clinically characterized TBE virus infections, 27 patients with antibodies against dengue or yellow fever virus and 100 healthy blood donors were investigated for anti-TBE virus antibodies. The assays yielded sensitivities of 91-95% and specificities of 91-94%. The test systems are valuable new tools for the diagnosis and monitoring of TBE virus infections.