This study assessed the analgesic action of tramadol compared with placebo in patients suffering from fibromyalgia syndrome. Twelve patients (11 females, one male) were treated according to a double-blind crossover experimental design. Each patient, after signing informed consent, was randomly allocated to either tramadol (100 mg ampul in 100 ml given intravenously in 15 min doses) or placebo for a single dose treatment. At the second visit, patients crossed over to the other drug for a further single dose treatment. There was a wash-out period of 1 week. Nine patients completed the study, while in three cases (two tramadol, one placebo) the study was discontinued due to the onset of side effects. The assessment of efficacy, carried out at the baseline and 15 min and 2 hours after administration of each dose, involved the use of a visual analog scale (VAS 100 mm) for spontaneous pain and pressure dolorimetry (kg/cm2) at 12 "symptomatic" tender points and nine "control" tender points for fibromyalgic pain. During the first treatment cycle effective control of spontaneous pain was achieved with tramadol, which determined a reduction of 20.6% while with the placebo spontaneous pain increased by 19.8%. With pressure dolorimetry there were no clinically important differences observed after either active treatment or placebo. The contrasting results found in the present study could be a stimulus for the organization of new projects, which may lead to the identification of an optimal therapeutic approach for fibromyalgic patients, also using tramadol for long periods.