The aim of this study was to verify the symmetry of cerebral blood flow changes during the generalized spike-wave discharges of typical absence seizures. A recording of mean flow velocity in the left and right middle cerebral arteries and of electroencephalographic activity was performed simultaneously in two subjects with multiple daily absence seizures. A total of 12 generalized spike-wave discharges were recorded. Mean flow velocities showed a significant increase during the discharges with respect to baseline. The increase of flow velocity started simultaneously or a few seconds before the discharges. In 91.6 % of all recordings, the percentage increase of mean flow velocity was significantly higher in the left than in the right side (7.03 % +/- 3.3 vs 5.14 % +/- 3.3; p < 0.1). The extent of the following decrease of flow velocity was also significantly greater in the left than in the right side (-16.91 % +/- 8.1 vs -14.07 % +/- 8.3; p < 0.01). These findings show an inter-hemispheric asymmetry in cerebral blood flow during generalized spike-wave discharges in two patients with absence seizures. Transcranial Doppler ultrasonography promises to be an interesting approach to detect rapid changes in cerebral hemispheric activity not otherwise recognizable.