My interest in pulsed electromagnetic energy a s a form of therapy goes back only 2 years. An initial investigation into its effects on the healing of recent soft tissue injuries demonstrated convincingly that it has a definite biologic action.’ More recently, 1 have made a comparative study between short-wave diathermy and pulsed electromagnetic energy in the treatment of ankle sprains. The results of this investigation show that in pairs of patients matched for sex, age, weight, and degree of trauma, conventional short-wave diathermy will produce a 44% recession of symptoms in 3 days by giving a total energy transfer of 22 W hr, whereas only 15 W hr of pulsed electromagnetic energy therapy results in a recession of 82% of symptoms during the same period. I consider that attempting to compare short-wave diathermy and pulsed electromagnetic energy is like comparing apples with oranges for sweetness. The value of the study was in demonstrating that when we used pulsed electromagnetic energy, a smaller quantity of energy produced very much better therapeutic results. This finding throws very considerable doubt on the theory that pulsed electromagnetic energy as a means of therapy is merely another method of generating heat i n the tissues. In attempting to find a more precise method of demonstrating the biologic effect of this technique, we decided to investigate its action on the rate of regeneration of peripheral nerves in experimental animals.