Blood sera from 151 dogs from areas of the Czech Republic endemic for human tickborne encephalitis (TBE) were examined for the presence of antibodies to TBE and West Nile (WN) flaviviruses by the haemagglutinationinhibition test. Antibodies to TBE virus at titres equal to or exceeding 40 were found in five dogs. Antibodies to WN virus were detected in only one dog that also had a high antibody titre to TBE, suggesting this was a crossreaction between the two closely related viruses. Three of the dogs (all rottweilers) with a TBE titre of 320 had clinical signs of meningoencephalitis or encephalitis. They all survived after treatment for the clinical signs. It was proved by seroconversion that the disease was caused by the TBE virus in one of these three dogs, and it seems very likely that the virus was responsible for the disease in the other two.