For over a decade, passive thermography has been utilized as a reasearch aid in the study of human breast cancerl . In this case, a passive thermographic system basically performs a spatial measurement of the 'natural thermal emission (heat) of the human body. The measured flux is then converted into an electrical signal, displayed, and recorded (generally on photographic film). Al-t hough passive thermography has proved to be of great value in diagnostic', work, there are limitations on its effectiveness. One such limitation is the thermographic system's inability to yield significant information relating to the depth of various portions of the breast's vascular tree. Efforts are currently in progress to overcome this problem by utilizing a technique called active-passive thermography. Before discussing this technique, the question of why the depth information is of importance is addressed.