The object of the proposed research is to continue investigating the effects of an applied electrical current and/or field on the acceleration of fracture healing in laboratory animals. The proposed research is designed 1) to determine the comparative effectiveness of direct constant and pulsed current, alternating current, electrostatic fields, and magnetically induced electrical fields in producing osteogenesis and in accelerating fracture healing in laboratory animals and 2) to determine the site and mechanism of action of electrical stimulation on medullary canal cells and on fracture callus cells. Methods to be used include point-counting analysis of histologic sections for new bone formation produced in an intact medullary canal around a cathode (negative electrode) in response to various parameters of current, voltage, electrostatic, and electromagnetic fields; mechanical testing for maximum resistance to bending of healing fractures in laboratory animals; point-counting analysis of electron micrographs of fracture callus cell in order to quantitate changes in cytoplasmic components; electron microscopy combined with histochemistry of fracture callus cells in order to detect changes in cell membrane surface charges; and determination of changes in tissue pO2, O2 consumption, and pCO2 by means of a tissue tonometer system.