Chronic pain, mysterious, invisible, complex. It destroys lives and causes unimaginable suffering. But now, we're on the verge of new understandings. Targeting the agony of cancer, watching the brain's response to pain, zapping the spinal cord with electrical current. These are just a few of the 21st Century weapons used against this ancient enemy. Pain specialists wage battle against chronic pain next, on ''Killing Pain.'' Okay, just relax and take some slow, deep breaths. Where are you hurting at, sir? Pain, we can't survive without it. When we break a leg or cut ourselves, the pain system sounds the alarm. When we come too close to a flame, the pain system warns us of danger. But for some people, the alarm never shuts off. You can't remember what life is without pain. My bones are made of glass, and all of a sudden they are hit with a baseball bat. Like being stabbed with a hot sword. The pain takes over, refusing to heal, destructive, cruel... You know, I was ready to just lay in bed, in pain, for the rest of my life. Chronic pain is not a symptom, but a disease itself. I mean, I've had broken bones and I've had babies and none of it's like this. This just keeps wearing on you. It makes you old. Until recently, chronic pain has been a mystery, to both patients and doctors.