Seven untreated patients with idiopathic generalized epilepsy were studied with recovery curve analysis using transcranial magnetic stimulation and compared with 16 controls. Patients had a shorter period of inhibition of the test response following a conditioning stimulus and demonstrated a period of increased facilitation of the test response at interstimulus intervals of 200 to 300 msec, which was similar to the mean interdischarge interval of spike-wave activity on EEG. This provides further evidence of cortical hyperexcitability in idiopathic generalized epilepsy.