Muscle atrophy, joint stiffness, osteoarthritis, infection, skin necrosis, atrophy and ulceration of joint cartilage and tendocutaneous adhesion are familiar complications produced by prolonged immobilization of surgically repaired tendon ruptures. Because these complications may be minimized by limited immobilization and early functional activities, we studied the effects of early weight bearing on the maximum breaking strength of tenotomized tendons in 30 Wistar rats. After tenotomy, the right hind limb of the first group of 10 rats was immobilized for the first 5 days. Thereafter their casts were removed to permit weight bearing for the next 3 days. In a second group of 10 rats, casts were removed 2 days after surgery, the animals were allowed 3 days of unrestricted use of the limb, and then the limbs were re-casted for another 3 days. In a third group of 10 rats the right hind limbs were casted throughout the first 8 days of healing. At the end of this time, strain gauge measurements showed that tendons in the second group healed significantly stronger and without rerupture than those in either of the two groups. Although healing time in rats does not directly translate to humans, our findings suggest that function may return faster in humans, as, for example, following Achilles tendon rupture, if a better combination of immobilization and activity could be found than is currently employed.