An external or internal torsional deformity of the femur was produced in twenty-two puppies by performing an osteotomy high in the femoral shaft between marker pins which were aligned to provide a permanent record of the amount of rotation resulting from the operation.

After sacrifice of the animals, two to five months later, the residual torsion of the osteotomized femur after this period of growth was determined by comparison with the torsion measured in the contralateral limb.

It was found that some degree of correction of torsional deformity occurred in all the animals with substantial growth. The average amount of external rotation produced at operation in fourteen animals was 43 degrees. The average residual torsion in this group at autopsy was 19 degrees, an average correction of 56 per cent. The comparable figures for eight puppies with internal torsional deformity were: an initial deformity of —33 degrees was found at autopsy to measure —14 degrees, a correction of 58 per cent. Most of the experimental femora showed mild asymmetry of the head. The findings in eight control animals with high femoralshaft osteotomy tended to verify the validity of the technique of measurement employed in the experiment.