This study was performed to test the existing notion that an increased muscle sympathetic nerve discharge is part of the underlying mechanism for the chronic pain syndrome of primary fibromyalgia. Muscle sympathetic nerve activity was recorded in the peroneal nerve in eight patients with primary fibromyalgia and eight age-matched controls. No difference in baseline sympathetic activity was observed between patients and controls. Furthermore, patients did not show exaggerated sympathetic nerve responses to static handgrip or jaw muscle contractions, postcontraction ischemia or mental stress. Thus the results do not indicate muscle sympathetic nerve overactivity in primary fibromyalgic patients.