Postexcitatory inhibition (pI) was studied in 13 patients with different clinical forms of Huntington's disease (HD), using a transcranial magnetic single and double stimulation paradigm. We found pathological results of pI in 77% of the HD patients. A significant prolongation of pI could be demonstrated in the group of patients suffering from a classical form of HD. In contrast to these patients, those patients suffering from primary rigid HD variants exhibited a shortening of pI. These results suggest an altered excitability of the motor cortex in HD according to dysfunctions within the motor cortex-basal ganglia loop. Transcranial double stimulation was a more sensitive measure in detecting changes of cortical excitation levels than single stimulation. The interpretation of pI changes in HD has to take the clinical subtype of HD into account.