Aims: The aim of this study was to test the hypothesis that temporomandibular joint (TMJ) pain is influenced by circulating levels of neuropeptide Y, serotonin, and interleukin-1B in rheumatoid arthritis. Methods: Forty-three seropositive (RF+) or seronegative (RF-) rheumatoid arthritis patients and 24 healthy individuals were included in the study. Results: High serum concentrations of serotonin were associated with low TMJ pressure pain thresholds and pain during mandibular movement in the RF+ patients. The results of this study do not support a relationship between circulating neuropeptide Y or interleukin-1B and TMJ pain. The RF+ patients had higher C-reactive protein levels and erythrocyte sedimentation rates than the RF- patients. There were also higher plasma levels of interleukin-1B in the RF+ patients than in the healthy individuals. Plasma levels of neuropeptide Y in the RF- patients were higher than in the healthy individuals. Conclusion: This study indicates that the serum concentration of serotonin is associated with TMJ allodynia in seropositive rheumatoid arthritis.