The first instrument of significance for the measurement of the temperature of the human body was the thermoscope, invented in 1502, probably by Galileo (1). Then followed numerous contributions by Huygens, Dalance, Roemer, Fahrenheit, Celcius, Boerhaave and de Haen, who made many modifications which led to the widespread measurement of temperatures in man. Improvements in the accuracy, types and reproducibility of heat detecting devices have continued through the years. Approximately fifteen years ago Doctor Ray Lawson performed his early investigations in the field of thermography and opened up the newest of the temperature recording techniques using a new device, the Thermograph. The purpose of this paper is to describe the use of the thermograph in the detection and evaluation of diseases of the cardiovascular system. METHOD Thermography is a scanning technique which gives a photographic display of point-to-point temperature differences of the surface of the body. The device consists of an infrared detector which is maximally sensitive to about 10 micron heat waves which emanate from the body. Variations in temperature produce voltage differences through the instrument that are proportional to surface temperatures. The voltage variations activate a light source which is mounted on a scanner; the light is focused on Polaroid film to produce a record in color or black and white. By use of a thermal scan consisting of a series of heat standards of known and constant temperatures, the temperatures of the part under study are determined by comparison of the degree of grayness of color. The device records surface temperatures; however, heat from deep structures such as from pelvic phlebitis, alters the deep and surface temperatures and thus may be recorded. The instrument can be set to detect differences in temperatures as little as 0.1 degree Centigrade which cannot be detected by palpation.Many excellent instruments are now available using color or black and white film which are suitable for static or dynamic studies of the circulation. In many cases moving pictures may be made easily or the picture may be stored, displayed in analog form, played back or computerized. There are many applications of thermography to the study of the circulation by the imaginative investigator.