Primary fibromyalgia (FM) is a painful condition, generally treated by analgesic drugs and antidepressants, which has been associated with hyperpyruvicemia and reduced high energy phosphate in muscle. Biological investigations were performed in patients with FM to determine whether this syndrome was related to carbohydrate metabolism impairment.Glycolysis was studied in 25 patients with FM, 10 patients with hypothyroidism (HO), 15 patients with osteoarticular chronic pain (OACP), and 36 healthy controls. Laboratory studies were performed on whole blood (pyruvate), erythrocytes (pyruvate kinase, 2-3 diphosphoglycerate, glyceraldehyde phosphodeshydrogenase, adenosine triphosphate), plasma and serum (lactate at rest and after forearm ischemic exercise, lactico deshydrogenase iso-enzymes).Comparisons between study groups and controls demonstrated increased pyruvate and decreased lactate production in FM and HO; adenosine triphosphate and muscular isoenzymes of lacticodeshydrogenase were decreased in FM only; glycolysis was not significantly impaired in OACP.These findings provide support that FM is associated with biochemical abnormalities which require appropriate metabolic therapy.