Fibromyalgia (FM) is characterized by chronic widespread pain lasting for a minimum of three months, and pain at mechanical pressure in at least 11 of the 18 tender points. The cause of fibromyalgia is unknown. Several hypotheses have been developed including "central sensitization". This theory proposes that fibromyalgia patients have a lower threshold for pain because of increased reactivity of pain sensitive neurons in the spinal cord or brain. Some researchers supposed that different neurotransmitters (serotonin, catecholamine) could be involved in the pathophysiology of fibromyalgia-associated symptoms. The connection of FM to different viral infections has been proposed. Epstein Barr Virus (EBV) has been considered a possible cause of FM because of similarity of symptoms, but so far, the connection has not been proven. The objective of this study was to determine the prevalence of antibodies (Abs) IgM and IgG against EBV, and respectively the presence of a viral infection in a group of patients with FM. We also analysed the association between the titter of the antiviral antibodies, some neurotransmitters (serotonin, noradrenaline and adrenaline) and different clinical symptoms. The obtained results revealed that high EBV IgG concentrations in the serum of patients with FM correlated with pain intensity and associated clinical symptoms. This is consistent with the fact that FM is connected to the immune response to certain infectious agents (e.g. EBV, CMV).