Residents (n = 497) of Central-Bohemian area affected by the 2002 flood were examined serologically for mosquito-borne viruses. Antibodies were detected against Tahyna (16%), Sindbis (1%) and Batai (0.2%) viruses, but not to West Nile virus. An examination of paired serum samples revealed one recent Tahyna bunyavirus (California group) infection. A natural focus of Valtice fever (Tahyna virus infection) was detected in the surroundings of Neratovice n.L.