1. Pronation of the foot is defined in terms of the prevailing imbalance of the foot while walking.

2. This definition is made possible by electrobasographic records of gait.

3. Twenty-four girls were studied with reference to the influence of shoes on balance of the foot while walking. Pronation was present in each case when street shoes of conventional design were worn. It was absent when the subjects wore shoes made to provide for balance of foot function in the stance phase of the step.

4. In these records, prevailing pronation is revealed by the overlap in weight-bearing time on heel and forefoot.

5. Under the influence of conventional shoes, normal feet may pronate while walking. Pronation brings strain on the whole locomotor mechanism, not on the foot alone.

6. The same feet do not pronate when the subject walks in shoes made to meet the requirements for foot balance in the stance phase of walking.

7. Normal balance of function of the extrinsic muscles, which support the bones of the foot in a tendinous sling, is the mechanism essential for protection against pronation and resulting strain.

8. The treatment of pronation, therefore, requires that consideration be given to the foot and the leg as a unit. Only through shoes which provide balance for the foot in the stance phase of gait can we compensate for malalignment of the os calcis with the tibia and the common contractures expressed through the tendo achillis.