This study investigated whether pain sensitivity of the pericranial musculature remains constant over the course of the day. Changes in the entire, uniformly metrically divided supra-threshold sensitivity range were measured. In 24 healthy volunteer subjects, pain was induced experimentally at 0200, 0600, 1000,1400, 1800, and 2200 hours in the pericranial musculature. Blood circulation in both superficial temporal and occipital arteries was reduced by applying a cuff to the head pumping up to 200 mmHg during rhythmic chewing on a spring, thereby producing a continuously increasing bilateral, dull, frontal headache. The subjects rated the intensity continuously using a category sub-dividing procedure ranging from pain threshold to pain tolerance limit. At low levels of headache intensity there were no significant diurnal differences in pain sensitivity. Sensitivity to very intense headache, however, varied significantly over the course of the day: sensitivity was greatest at 0200 hours; it decreased at a constant rate until1400 hours, and increased again continuously until 2200 hours (pó.05). Also the findings showed significant effects of sex on the pain sensitivity of pericranial musculature for all pain intensities: women are approx. twice as sensitive as men (pó.0.05). These results suggest that not only sex, but also time of day, must be taken into consideration in the clinical determination of pain sensitivity of pericranial musculature in the course of headache diagnostics.