Early (ES1) and late (ES2) exteroceptive suppression periods elicited by electrical stimulation of the labial commissure during teeth-clenching were recorded over the temporalis muscle in 45 headache patients (25 tension headaches and 20 migraines) and 22 controls. Mean duration of ES2 for single shocks was significantly reduced in tension headache when compared with migraine or controls. At a stimulation rate of 2 Hz, ES2 was abolished in 40% of tension headache sufferers, but in none of the migraineurs. EMG analysis of temporalis late exteroceptive suppression might be a helpful diagnostic tool in functional headaches. Reduction of ES2 suggests that there is deficient activation or excessive inhibition of pontobulbar inhibitory interneurons which receive a strong input from limbic structures. ES2 might thus represent an interface between psychogenic and myogenic factors putatively involved in the pathogenesis of tension headache.