We treated fifty-one cases of fracture of the shaft of the humerus with a functional method of treatment consisting of a plastic sleeve, individually molded or prefabricated. It maintained good alignment of the fragments and permitted rapid and uninterrupted osteogenesis. The early introduction of functional activity to the entire extremity appears to provide a desirable physiological environment conducive to rapid healing. Non-unions have not been encountered in nonpathological fractures. Healing time has been rapid, and there has been consistent restoration of motion of all joints prior to the completion of healing. The morbidity was minimum.