Abstract Injecting a local anesthetic mixed with a radiopaque solution permitted the course of the mandibular block to be traced with cephalograms. This technique also permitted a study of the anatomy of the pterygomandibular space and the success of anesthesia correlated with needle position. Much of the anesthetic solution may exit the space and still give excellent anesthesia; only a small part of the Xylocaine in a Carpule is seemingly necessary to produce insensitivity if it encounters the nerve somewhere along its course. Injections posterior to the foramen should be avoided to increase the chance of obtaining clinical anesthesia. Placement of the needle tip superior to the mandibular foramen gave good anesthesia in most injections; however, research on a large series of subjects might indicate better anesthetic success with injections made inferior to the foramen.