Negative pi mesons have been proposed as a modality for tumor therapy. They have many possible advantages over other modalities. One of these is the possibility of in situ monitoring of the treatment volume. Three methods of doing this have been proposed. Two of the methods involve nuclear γ-rays and the production of positron emitters. Preliminary experiments designed to test the concepts involved in these methods have been reported. This paper reports the results of an experiment to test the third method. A beam of π- mesons was stopped in water, and the mesic x-rays were detected with a position-sensitive detector (Anger camera). All three methods are discussed.