The amplitude of electrical potentials generated in stressed bone is dependent upon the rate and magnitude of bony deformation, while polarity is determined by the direction of bending. Areas under compression develop negative potentials with respect to other areas. Similar results were obtained both in living and dead bone. Removal of the inorganic fraction from bone abolishes its ability to generate stress potentials. It is probable that these potentials influence the activity of osseous cells directly. Furthermore, it is conceivable that they may direct, in some manner, the aggregation pattern of the macromolecules of the extracellular matrix.