Oral administration of zolmitriptan, a novel 5-hydroxytriptamine receptor agonist, to eight healthy volunteers significantly reduced motor cortical excitability as tested by paired transcranial magnetic stimulation (TMS) at short interstimulus intervals. Zolmitriptan did not change motor thresholds to TMS or electromyographic silent period durations. We conclude that zolmitriptan acts centrally by reducing the inhibition within the motor cortex. The results suggest that the action of zolmitriptan on motor cortical excitability does not result from changes at the level of the cell membrane but from the influence on GABAergic inhibitory interneurons.