A method of detecting the amount of heat produced by different parts of the body. This is done with an infra-red sensitive photographic film. High blood flow in an area shows up as a heat zone and thus tumours such as breast cancer can be identified. The process records such changes in temperature in a record known as a thermogram. Unfortunately, such hot areas of skin are caused by a number of other conditions; this is therefore a diagnostic method that can be used only as a rough screening procedure.