It has recently been reported that the pericranial muscles in patients with chronic tension-type headache are harder, i.e. have a higher consistency, than in controls. The primary aim of the present study was to investigate whether muscle hardness is influenced by the presence or absence of actual headache and whether hardness is correlated to tenderness. The secondary aim was to compare muscle hardness between patients and healthy controls. Hardness of the trapezius muscle was measured with a hardness meter in 20 patients with chronic tension-type headache and in 20 healthy controls. The patients were examined on 2 days, 1 day with headache and 1 day without headache. Pericranial myofascial tenderness was recorded with manual palpation. In addition, muscle hardness was measured in another five patients out-side headache and in 30 healthy controls. The muscle hardness recorded in patients (n = 20) on days with headache, 98 +/- 26 kPa/cm, did not differ significantly from the muscle hardness recorded on days without headache, 100 +/- 21 kPa/cm, (P = 0.62). The muscle hardness was positively correlated to the local tenderness score recorded from the trapezius muscle both on days with headache (R = 0.52, P = 0.02) and on days without headache (R = 0.53, P = 0.02). The total tenderness score (TTS) recorded in patients on days with headache, 23 +/- 10, was significantly higher than the TTS recorded on days without headache, 15 +/- 11, (P = 0.0001). There was a significant difference between the TTS recorded in patients without headache, 15 +/- 11, and in controls, 4 +/- 4, (P = 0.002). The muscle hardness was significantly higher in patients on days without headache (n = 25), 97 +/- 20 kPa/cm, than in controls (n = 30), 87 +/- 16 kPa/cm (P = 0.03). On basis of previous and present results, we suggest that muscle hardness and muscle tenderness are permanently altered in chronic tension-type headache and not only a consequence of actual pain. In addition, the positive correlation between muscle hardness and tenderness supports the common clinical observation that tender muscles are harder than normal muscles.