1. No transected anterior cruciate ligament healed unless the ligament ends were held in complete apposition by suture.

2. Excessive tension on the suture line of the primarily repaired anterior cruciate ligament resulted in necrosis of the ligament and failure of the repair.

3. The divided anterior cruciate ligament in thirty consecutive dogs healed when treated by surgical repair apposing the severed ends under proper tension.

4. Prompt absorption and shortening of the ligament followed section of the anterior cruciate ligament without repair to the extent that apposition was impossible as early as two weeks after section.

5. Sectioned and repaired anterior cruciate ligaments showed microscopic evidence of complete fibrous healing by ten weeks, but there was still minimum residual fibroblastic activity at this time.

6. Tensile strength of the healed repaired ligament remained substantially less than that of normal ligaments at ten weeks.

7. When the anterior cruciate ligament was replaced with a graft composed of the iliotibial tract, a fibroblastic response occurred throughout the entire graft. It may be this response that converts the graft into a ligamentous structure.

8. The grafts were shown to survive as ligamentous structure up to four years after operation.

9. In our series the reconstructed ligament did not seem to provide stability comparable with that provided by the healed primarily repaired ligament, but there were insufficient animals in this series to reach valid conclusions in this regard.