AbstractObjective. To investigate the in vivo and in vitro expression of somatostatin receptors (SS‐R) on synovial membranes of patients with rheumatoid arthritis (RA).Methods. The joints of 14 consecutive patients with active RA, 4 patients with severe osteoarthritis (OA), and 30 control patients were studied. The somatostatin analog [111In‐DTPA‐D‐Phe1]‐octreotide was used for in vivo SS‐R scintigraphy, and the somatostatin analog [125I‐Tyr3]‐octreotide for in vitro SS‐R autoradiography.Results. Seventy‐six percent (220 of 290) of the painful joints and 76% (207 of 274) of the swollen joints of the patients with RA were visualized by SS‐R scintigraphy. The degree of pain and swelling correlated well with positive scintigraphy findings in the joints (P < 0.0001). In 2 of the RA patients who underwent scintigraphy, as well as in 4 of 5 other patients, in vitro studies of the synovial membranes showed the presence of specific SS‐R. In patients with OA, uptake of radioactivity in the affected joints was significantly lower than that in patients with RA. None of the joints of the control patients demonstrated uptake of radioactivity.Conclusion. SS‐R are present in the synovial tissue of patients with active RA, as demonstrated by both in vivo and in vitro techniques. The potential value of SS‐R scintigraphy in the clinical evaluation of patients with active RA is presently unknown.