In late cases of Kienböck's disease in which the lunate is diminished in size, implant arthroplasty cannot give good results. Carroll developed the autogenous tendon graft in 1970. We have utilized this technique in 35 cases with generally satisfactory results. In order to clarify the rationale of this procedure, the fate of the packed free tendon was studied experimentally using four rhesus monkeys and 40 rabbits. The animals were serially sacrificed, and observations were made, revealing that the packed tendon moulded itself to the surrounding articular surfaces. Histologically, it became gradually collagenized and finally hyalinized, to act as a good spacer.