We observed a marked prolongation of the transcranially evoked silent period during continuous intrathecal administration of high doses of the gamma-aminobutyric acid (GABA)B receptor agonist baclofen in a patient with generalized dystonia. Size of motor evoked potentials and central conduction time remained unchanged during intrathecal baclofen administration. The selective prolongation of the silent period during high-dose continuous intrathecal baclofen therapy supports the notion that GABA(B)-ergic intracortical interneurons play a part in the generation of the transcranially evoked silent period.