The effect of S-adenosylmethionine (SAMe) and placebo was evaluated in a short-term crossover study of 17 patients with primary fibromyalgia. Eleven of 17 patients had a significant depressive state as assessed by either the Hamilton Depression Rating Scale or the Scala di Autovalutazione per la Depressione (SAD) rating scale. The number of trigger points plus painful anatomic sites decreased after administration of SAMe (p less than 0.02) but not after placebo treatment. In addition, scores on both the Hamilton and SAD rating scales improved after SAMe administration (p less than 0.05 and p less than 0.005, respectively), whereas they did not significantly change after placebo treatment. In all the patients, there was a good correlation between scores on the Hamilton rating scale and the number of trigger points. Thus, this preliminary study confirms the close relationship between primary fibromyalgia and psychologic disturbances, particularly with regards to a depressive state. SAMe treatment, by improving the depressive state and reducing the number of trigger points, seems to be an effective and safe therapy in the management of primary fibromyalgia.