This study compared the effects of postoperative immobilization and early controlled passive motion on tensile properties of healing chicken flexor tendons during the initial 30 postoperative days. Results indicate (1) that controlled passive motion tendons had significantly greater values for rupture load, stress, and energy absorbed; (2) that both groups showed significant, and predictable changes, in strain, stiffness, and stress across this healing period; and (3) that there was no difference between the groups in rate of change for any of the tensile properties examined. These findings suggest that not only does early controlled passive motion not interfere with rate of early flexor tendon healing, but that early controlled passive motion may improve healing efficiency.