Hot water epilepsy (HWE) was induced in freely moving Wistar rats by applying hot water jets over the head region. The status of the blood-brain barrier (BBB) during the seizures and during hot water-induced hyperthermia without seizures was examined using Evans blue dye. In order to investigate the contribution of concomitant factors to this process, synchronized body temperature and blood pressure recordings were also made. Tonic-clonic seizure activity was observed within an average of 3.9 min (SE=0.6 min) in the rats exposed to the hot water jets; this treatment induced BBB opening in the cortical and deep brain areas. Body temperature and blood pressure increased from 36.5degrees +/- 0.3 degreesC to 40.0degrees +/- 0.2 degreesC, and from 91 +/- 3 mmHg to 153 +/- 4 mmHg, respectively. In the group of animals exposed to hot water application without inducing seizures, there were significant increases both in blood pressure and body temperature; however, the extravasation of Evans blue was not pronounced in the brains. Hot water-induced seizures, increased cerebrovascular permeability. Although high blood pressure and hyperthermia contribute to this permeability, the seizure activity is the major factor in this change.