The path a meridian follows as it runs through the body (as well as the location of the points along the meridian) is also used to help diagnose and treat illnesses. For example, LI-4 is known to treat disorders as diverse as the common cold, toothache, stuffy nose, nosebleed, delayed labor, deafness, mumps, excessive sweating or lack of sweat, neck pain, and red-teary-swollen eyes. These are known as channel symptoms and are tied together diagnostically by the fact that the Large Intestine meridian runs through each of the areas affected.

Disorders of the meridians themselves can also be used diagnostically, as pain along the course of a channel will sometimes indicate dysfunction of its related organ. Again reinforcing the clinical usefulness of knowing the meridian system, we also find that localized pain can often be treated by needling points farther up or down the meridian. Meridian theory is truly one of TCM's strongest advantages over the compartmentalized view of the body we inherit from Western medical theory.