In thirty-eight dogs anterior cruciate repairs were performed and in twenty dogs anterior cruciate reconstructions using the iliotibial band were done. The results were studied for six months to four years postoperatively to determine tensile strength and microscopic anatomy. The results were as follows:

1. Ultimate resorption of the repaired ligaments was not uncommon, occurring in fourteen of thirty-six repairs.

2. Repaired ligaments which maintained tensile strength also tended to maintain joint stability.

3. Anterior cruciate ligaments repaired with wire showed a progressive increase in strength compared with the ligaments repaired with silk.

4. The incidence of persistent inflammatory changes was much higher in anterior cruciate ligaments repaired with silk compared with those repaired with wire.

5. Anterior-cruciate reconstructions using the iliotibial band tended to lose strength and stability with time.

6. Persistence of marked inflammatory changes in reconstructed ligaments was associated with decreased tensile strength. Persistence of the fibroblastic proliferation, on the other hand, even as late as three years after operation, was found in the strongest reconstructions.

7. The constant association of degenerative changes with instability found in the knees of the dogs in this series tends to confirm the opinion that knee-joint instability uncorrected ultimately leads to degenerative changes in the joint.