Inhibition of the second exteroceptive suppression of temporalis muscle activity (ES2) produced by a preceding electrical stimulus applied at the index was studied in patients suffering from migraine without aura (MO), chronic (CTH) or episodic (ETH) tension-type headache. Each patient group comprised of 12 subjects was compared to a group of healthy controls. Mean duration of unconditioned ES2, measured on 10 averaged rectified responses after labial stimulation at a 0.1 Hz frequency, was reduced in CTH only. From stimulation intensities of 20 mA onward, peripheral-induced inhibition of temporalis ES2 was significantly more pronounced in both subtypes of tension-type headache compared to migraineurs or controls. After an index finger stimulus of 20 mA, temporalis ES2 was abolished in 83% of CTH, 67% of ETH, 25% of MO patients and 8% of controls, whereas unconditioned ES2 was present in all patients. Among 9 ETH patients with normal (> or = 32 msec) unconditioned ES2, 5 had total disappearance of ES2 after a 20 mA index stimulation. These results demonstrate that peripheral conditioning at 20 mA increases the diagnostic sensitivity of ES2 studies. They suggest that the changes observed in tension-type headache are due to hyperexcitability of the reticular nuclei which inhibit the medullary inhibitory interneurons mediating ES2.