BACKGROUND: The transplantation of adrenal medullary tissue into the CNS of the rat can reduce pain. This results from the release of opioid peptides and catecholamines from the transplanted chromaffin cells. However, whether the adrenal gland transplanted in peripheral tissue can also reduce the pain is not well documented. The purpose of this study was to assess the potential for theadrenal gland implanted into the peripheral tissue of the rat to reduce mechanical hyperalgesia induced by inflammation. METHODS: Fifteen male Wistar rats were divided into three groups; one for implantation of the adrenal gland (AG), another for the kidney (Kd), and the other for a Sham operation (S). Tissues for transplantation were harvested from Sprague-Dawley rats. Two weeks after surgery, inflammation was induced by injecting 0.05 ml of Freund's Complete Adjuvant (FCA) into the dorsum of the rat's hind paw. Mechanical hyperalgesia was assessed using automated Randall-Sellito algesiometer at 6 hr, 1, 2, 3, 7 and 14 days after injecting FCA. RESULTS: Paw withdrawal thresholds against mechanical stimuli were 84.8 6.9%, 112.1 4.6%, 86.3 8.5%, 93.6 7.4%, 90.5 3.8%, 96.9 3.8%, respectively, in the AG group, and 71.3 10.8%, 93.3 11.3%, 79.1 10.3%, 73.7 8.1%, 62.6 6.4%, 77.7 6.2%, respectively, in Kd group, and 67.2 8.3%, 88.1 11.7%, 67.7 8.1%, 69.6 8.2%, 74.5 8.5%, 81.2 6.6%, respectively, in the S group. The AG group showed less pain sensitivity compared with that of the Kd and S groups especially 7 and 14 days after injecting the drug. CONCLUSIONS: This study indicates that the transplanted adrenal gland into the peripheral tissue may provide analgesic effect for a long time after it is transplanted in the rat.