The purpose of this study was to investigate the biomechanical and histological features of patellar tendon-bone autografting and free flexor-tendon autografting, which were fixed by two different techniques at the tendon-bone junction in reconstruction of an infraspinatus defect in sheep. Merino type sheep ( n=10) were divided into two groups. Following a defect in the infraspinatus tendon, in group I (flexor-tendon autografting) the free end of the flexor tendon was passed through the holes in the greater tuberosity for fixation. In group II (patellar tendon-bone autografting), fixation was obtained by impaction of the tibial bone plug to the greater tuberosity. Twelve weeks later, animals were sacrificed and specimens were evaluated biomechanically and histologically. Recovery of tensile mechanical properties was achieved to a level of approximately 50% in Group I and 70% in Group II at the end of the 12th week. No difference in the stiffness values was found. In group I, there was a difference between operated and contralateral (non-operated) tendons for the ultimate tensile strength values, but no difference was found in group II. Histologically, in group I, the defective area, which filled with a hypercellular connective tissue, could hardly be differentiated from the normal tendon tissue. In group II, complete incorporation of the bone block was seen in all specimens. These results suggested that patellar tendon-bone autografting is more advantageous than free flexor-tendon autografting in infraspinatus defect, providing rapid healing and better mechanical properties, especially in the early period of healing.