fibromyalgia is one of the commonest rheumatic symptoms, characterized by musculoskeletal pain and painful points with neither synovitis nor myositis. 20 patients with diagnosis of fibromyalgia were studied to know the alterations of the autonomous nervous system by the ergometric test. in the control group, it was observed a normal increase of frequency on adopting orthostatism, which reflects the activation of the sympathetic system. this reflex did not exist among the patients with fibromyalgia. an adequate rise of the arterial pressure in 87 % of the patients with fibromyalgia, an infraunevenness of the st over 1 mm in 20 % of the patients, an absence of arrhytmia and symptoms of heart disease in all patients, and a reduction of physical capacity in 4, were proved. it was concluded that patients with fibromyalgia present a dysfunction of the autonomous nervous system.