The results of reconstruction of flexor tendons of the hand are not satisfactory despite many operative methods. Since 70 years different surgical methods were described from which only some found application and some are tested up to day. The classical surgical methods do not prevent adhesions of tendons to the surrounding tissues. Therefore studies were undertaken to proof the usefullnes and the specific properties of silicone fluids in the reconstructive tendon surgery. Examinations were done on 48 mongrel rabbits of both sexes on surgically exposed tendon of the gastrocnemius muscle. The animals were divided into two groups. In group I the tendon of the right extremity was covered with Medical Fluid 360, and in group II - with Silol F 350. Each group was divided into two subgroups. In subgroups IA and IIA the tendinous sheath was removed whereas in subgroups IB and IIB the tendon was also cut and sutured. The silicone fluids were spread in amount up to 1 ccm, and uniform coat on tendon surface resulted. On the left tendons 0.9% natrium chloride solution was spread for control. In both groups the dissections were performed 14, 30, 90, 180 days after the operation. The following criteria were applied to evaluate the results: - the appearance of extremities, the range of motility in knee and ankle joint, wound healing, - the macroscopic appearance of isolated tendons, - the degree of excursion measured in millimeters, - the appearance and degree of adhesion between the tendon and surrounding tissues. 800 histological preparations were made. They were evaluated in biological microscope with special attention to the dimension of tissue reaction. In histological examinations the differences in tissue reaction were stated between subgroups A and B of both groups. However, no differences were found dependent from the applied silicone in groups I and II. In the early period, around the siliconized tendon poorly cellular, not significant exudative reaction was found. This reaction changed afterwards into proliferative one, which led to the development of a new tendon sheath. These changes did not discriminate distinctly the flexibility of the examined tendon. After applying 0.9% natrium chloride solution to uncovered tendon (control), adhesions of the tendon to surroundings were observed, which resulted in discrimination of tendon's flexibility. It was proved that silicone fluids applied to the sutured tendon (groups IB and IIB) did not handicap the healing process. The peritendinous adhesions were more intensive around the tendon's anastomosis than in the remaining tendon part. These adhesions were significantly smaller in comparison with the control extremities whose tendons were covered by0.9% natrium chloride solution. The application of small quantity of silicone fluids according to both up to day and own investigations do not cause local or general pathological changes...