During 1997-2002, a total of 417 patients presenting clinical signs and symptoms of DF were examined in the Czech Republic. Anti-dengue antibodies were assessed by ELISA, using PANBIO kits (Brisbane, Australia). The specific lgM and lgG antibodies against DF were detected with the use of the Dengue lgM Capture ELISA Test and Dengue Indirect lgG ELISA Test, respectively. When the absorbance values were higher than the cutoff +10%, the sample was considered to be positive, which was in agreement with a relative value of 200 or higher. Since 2002, the results of the quantitative antibody examination have also been expressed in EU (ELISA UNITS) on the following scale: 11 EU, positive result.