(1) Repairing surface structure of transected digital flexor tendons of hens were studied by scanning electron microscopy. One week after a simple suture, fibrous materials probably of fibrin and exudated blood cells were attached on the surface. After two weeks, lining cells enmeshed with fine fibrils covered most of the surface. After three weeks, cellular protrusions of spindle shape spread over the repaired tendon. (2) Repaired surface of partially resected tendons of hens showed the same sort of healing processes as observed in the sutured tendons. The injured tendon surface was covered with the lining cells derived from surrounding synovium. (3) It was suggested that the repair of the injured tendons may occur from the surrounding tenosynovium, where the fibroplastic-like lining cells cover the injured part. (4) Observation of surface structure of pseudosheath was carried out after the silicone rod implantation with complete resection of the surrounding sheath. In one or two weeks, spindle-like cells probably corresponding to fibroblasts appeared on the surface. Fibrillar substance also mingled with such fibroblastic cell protrusions. Well-repaired pseudosheath similar to the normal parietal sheath was seen at four weeks. Such differentiated synovial lining cells formed from the peritendinous tissues were also regenerated from the original area around this time. (5) It could be said that the experimental repair on the visceral and parietal layer of the tendon sheath was similar in time and form. However, it seems to be necessary to compare the results from human subjects in relation to the abnormal repair of the injured tendon such as in adhesions.