Patients with a chronic pain syndrome often suffer from sleep disturbance. As both symptoms are frequent in the fibromyalgia syndrome, these patients in particular have been examined in this regard. No clear polysomnographic evaluation of the subjectively experienced sleep disturbance in these patients has been done so far. Therefore, we recorded the sleep EEG of 13 patients with a fibromyalgia syndrome in order to objectively characterize their sleep. Furthermore, we were interested in the relationship between the sleep alterations and pain intensity. In a subsequent placebo-controlled study based on pathophysiological considerations, we attempted to beneficially influence the sleep disturbance and the pain syndrome with the 5-HT2-receptor antagonist ketanserine, as this system has been proved to play a major role in the regulation of both sleep and pain. The results of our studies in patients with fibromyalgia show that the alteration of sleep is mainly characterized by a disturbance of sleep continuity associated with the experience of pain intensity. The application of 5-HT-receptor-antagonists may be a new strategy for the common treatment of sleep disturbance and the pain syndrome which needs to be evaluated in further studies. Duration of the patients' illness seems to be a predictive value in relation to intensity of the symptoms and the therapeutic outcome.