Low-energy, pulsed electromagnetic fields (PEMFs) have reversed therapeutically resistant pathologic processes in the musculo-skeletal system. Their development as a non-thermal therapeutic agent is based on 30 years of study of the electro-biological properties of connective tissues. Specific energy characteristics in applied PEMFs produce selected biological effects by modifying synthetic and other behavioral patterns of target cells; some mechanisms of action are defined. The technology appears safe and effective in clinical treatment of un-united fractures, avascular necrosis of bone, and chronic, refractory tendinitis. An expanding, rational use in biomedical science is predicted.