BACKGROUND: We have paid more attention on the effects of growth factors on tendon healing and adhesion formation, especially on the correlation of transforming growth factor with tissue adhesion and scar formation. OBJECTIVE: To investigate the expression of transforming growth factor beta-1 mRNA in the zone Ⅱ flexor tendon of wound-healing rabbit models. DESIGN: Randomized controlled animal study. SETTING: Department of Orthopaedics, Affiliated Hospital of Medical College, Qingdao University. MATERIALS: Sixty clean adult New Zealand white rabbits weighting 4.0-4.5 kg, of either sex, were provided by Qingdao Animal Experimental Center. Left forelimbs of each animal were as experimental side, and right forelimbs of each animal were as control. There were 6 time points, namely at days 1, 7, 14, 21, 28 and 56, 10 rabbits in each time point. Of the 10 rabbits, 6 rabbits received the in situ hybridization and 4 rabbits received the immunohistochemical staining. Animal intervention met the animal ethical standard. METHODS: Experiments were performed at the Animal Experimental Center of Hospital Affiliated to Medical College of Qingdao University from September 2005 to July 2006. After anesthesia, each rabbit underwent complete transection of the profundus middle flexor tendon in zone Ⅱ, and then the tendon was repaired by the Kessler method. Rabbits in the control group did not receive any intervention. Rabbits were anesthetized and killed 1, 7, 14, 21, 28 and 56 days after the surgery. Skin was incised along the original incision at the experimental sides to obtain tendons and tendon sheaths. The same measurements were performed in the control group. MAIN OUTCOME MEASURES: Tenocytes and tendon sheath cells were detected with the in situ hybridization and the immunohistochemical staining to observe the expression of transforming growth factor beta-1. RESULTS: Sixty rabbits were involved in the result analysis. ①The in situ hybridization results: Expression of transforming growth factor beta-1 mRNA was increased at day 1 after tendon injury in the experimental group, reached a peak at days 14-21 after tendon injury, reduced at day 28 and was still in a high level at day 56. Expression of transforming growth factor beta-1 mRNA was high in tendon sheath cells around the repaired region. At the same time point, the expression of transforming growth factor beta-1 mRNA was higher in tendon sheath cells than in tenocytes. Low expression of transforming growth factor beta-1 mRNA was found in tenocytes and tendon sheath cells in the control group. The expression of transforming growth factor beta-1 mRNA in tenocytes and tendon sheath cells was higher in the experimental group than in the control group at each time point (P ＜ 0.05). ②Immunohistochemical staining results: Expression of transforming growth factor beta-1 protein was elevated at day 1 after the surgery, reached the peak at days 14-21 and was still in a high level at day 56 in the experimental group. Low expression of transforming growth factor beta-1 protein was seen in the control group. CONCLUSION: The normal uninjured tenocytes and tendon sheath cells produce transforming growth factor beta-1. The cytokine is activated in the injured tendon. The increase of this cytokine in both tenocytes and tendon sheath fibroblasts are coincidence with both extrinsic and intrinsic mechanisms for tendon repair.