duced: FSME-IMMUN (Pfizer, USA), prepared from the Neudoerfl strain of the European subtype (Barrett et al., 2003), and Encepur (GSK), based on the Karlsruhe (K23) strain (Harabacz et al., 1992;Girgsdies and Rosenkranz, 1996). These vaccines have been used for more than 30 years and are highly effective in preventing TBE (Barrett et al., 2003).Contamination of the product during the manufacturing process with pyrogenic material, which may originate from growth of contaminating bacteria or as carry over of an unsuccessful purification step, must be avoided and, accordingly, vaccines as well as all other parenteral medicines are tested for pyrogens. These fever-inducing substances are derived from Gram-negative and Gram-positive bacteria (endotoxin, lipoteichoic acid), viruses,