After a brief review of thermal physics and physiology, the authors explain the applications of cholesterol ester plates in the study of breast malignancy. Accumulated experience plus the fruits of statistical studies conducted in leading centers, make it advantageous to use contact thermography not only for the early diagnosis of breast malignancy but also for mass screening of the general population. In competent hands, this technic yields accurate and dependable diagnosis; the method is completely harmless to patient and physician and can be used as many times as needed; and in addition, the method is economical both in terms of time consumed and of actual cost of materials. The new method does not supersede roentgenological investigation indiscriminately but confines it to cases that remain doubtful or suspicious after clinical and thermographic examination.