Dotarizine is chemically related to calcium antagonist cinnarizine and flunarizine. The study presented investigates the influence of the drug on the diameter of cortical arteries and cerebral blood velocity measured in the MCA in two groups of anaesthetized cats. Changes of vessel diameter were measured indirectly using photographs of the cerebral cortex during experiments, and flow velocity was measured using transcranial Doppler sonography. Dotarizine was administrated by 20 minute intravenous infusion in a dose of 0.05 mg/kg/min. In the first group of animals the infusion was started during normoventilation, in the next group the infusion started during 30th minute of hyperventilation. The most conspicuous data were obtained in experiments conducted in hyperventilated animals where dotarizine abolished the vasoconstrictive effect of hyperventilation. The results suggest that dotarizine has a pronounced effect on basal as well as cortical arteries of the brain.