Transcutaneous electrical stimulation appears to be a valid technique for the treatment of many pain states. Its use in chronic pain is limited and it appears to be much more likely to be effective in the relief of acute painful states. Nevertheless, since it provides a simple way to treat a significant number of patients whose pain would otherwise by intractable, it has been a valuable addition to the armamentarium of the physician dealing with chronic pain. Peripheral nerve stimulation is an excellent way to relieve pain of peripheral nerve injury origin and certain painful, poorly understood, vasopastic or reflex sympathetic states. Spinal cord stimulation has been revived by the advent of percutaneous stimulators. The technique is currently the best available for the treatment of the patient suffering from the chronic low back syndrome with severe arachnoiditis, for whom no definitive therapy is available. Brain stimulation has been relegated to therapy for pain of central nervous system origin. It is a most promising technique though its application appears to be limited at this point to a few specific problems. The seriousness of potential complications has kept it from being widely applicable to date. There is little information concerning the mechanism whereby these various techniques are effective. Transcutaneous and peripheral nerve stimulation might have their effect through peripheral mechanisms or through a gating mechanism in the posterior horn (Melzack and Wall 1965; Campbell and Taub 1973). Spinal cord stimulation could act through a retrograde effect upon a dorsal horn gate or have more central actions. Brain stimulation in the opiate receptor system may be effective through activation of this system. The mechanisms of action of stimulation in the sensory system centrally are certainly not well understood (Bloedel 1974).