We studied vestibulo-ocular reflex measurements in a group of 12 patients suffering from migraine without aura and evaluated the effect of sodium valproate given as prophylactic migraine therapy. The study was randomized, double blind and placebo controlled, with a crossover design. The horizontal vestibulo-ocular reflex was evaluated by the Sinusoidal Harmonic Acceleration test at 0.01, 0.02, 0.04, 0.08end 0.16 Hz using a computerized rotatory chair system. No abnormalities were found for the vestibulo-ocular reflex gain, phase and asymmetry at each of the frequencies examined during the placebotreatment. These normal vestibulo-ocular reflex measurements contrasted with the repeated complaints of dizziness, vertigo and unsteadiness reported by 7 patients (58%). Sodium valproate affected neither vestibulo-ocular responses nor vestibular complaints but was effective in reducing migraine attacks in 8 of the 12 patients. These results demonstrate that the low frequency vestibulo-ocular reflex measurements are normal in patients suffering from migraine without aura.