Flexor tendons were harvested from donor dogs, freeze-dried, and reimplanted into six mongrel dogs that were made surgically anterior cruciate ligament (ACL) deficient. After one month of immobilization the dogs were allowed to run free for eight months. At this time all ACL substitutes were found to be intact and repopulated by host cells. Mechanical testing showed the freeze-dried allograft ACL to be significantly weaker than the normal control ligament but similar in strength to implanted tendon autograft ligament substitutes.