The effects of controlled passive motion on primary tendon repair were studied using the canine forepaw flexor apparatus as experimental model. The animals were divided into seven groups based on duration(3 to 12 weeks post repair) and mode of immobilization and partial mobilization. The repaired tendons were subjected to biomechanical evaluation of their gliding function and tensile strength characteristics. The results showed positive effects of controlled passive motion on tendon repair. The rate of tendon repair was significantly improved over those animals that were continuously immobilized. At 12 weeks, the repaired flexors from the motion group had regained over one-third of the ultimate tensile load as compared to their contralateral intact controls. Of equal importance is that these repaired tendons maintained good gliding function within the sheath during the repair process. The gliding function of these tendons was also significantly better than those subjected to continuous immobilization.