The presence of clinical and electromyographic (EMG) features of neuromuscular hyperexcitability (NMHE) and of the commonly associated neurovegetative disturbances (NVD) were investigated in 49 patients with primary fibromyalgia (PF) and in a control group of 33 patients with rheumatoid arthritis (RA). At least two clinical features of NMHE were present in 39%, and at least three NVD in 63% of PF patients. In contrast, only 1 RA control had two NMHE features (p greater than 0.005) and three NVD (p less than 0.001). Moreover, a significant post-ischemic spontaneous EMG hyperactivity was observed in 11 PF patients, and in only 1 control with RA (p less than 0.05). Finally, in patients with PF the number of tender points were correlated with psychological tests for depression (p less than 0.02), and the number of NVD. The present study shows that in patients with PF there is a large prevalence of NMHE complaints and NVD. The potential underlying pathogenetic mechanisms are also discussed.