Thus did the late, great humanitarian, Albert Schweitzer, elegantly characterize pain and what he perceived to be his role in effectively relieving it. Certainly, the relief of pain has always been one of the most important reasons for the existence of the physician, and even today, one of our most important raisons d'être. Therefore, ample comprehension of pain and its mechanisms is an essential prerequisite for optimal application of the therapeutic strategies currently available to prevent or eliminate acute and chronic pain. In its acute symptomatic form, pain has an important biologic function: it warns the individual of a disease or injury and prompts the patient to seek medical help, and it also serves as a useful diagnostic aid to the physician. After appropriate therapy that effectively eliminates the disease or the injury, the pathologic processes and the associated pain regress and finally disappear. In contrast, in its chronic, persistent form, pain has no biologic value, but is rather a malefic pathologic process