A method and apparatus for the noninvasive detection of a concentration of a substance in a body, such as glucose in the human bloodstream is disclosed. The apparatus measures substance concentration by detecting radiation in the far infrared range emitted by the body using an infrared detected in combination with a set of adequate filters. In order to achieve the accuracy required, the radiation values detected by the detector arc corrected for the emissions of the system components. The temperature of each system component including the detector temperature and an ambient temperate is determined using temperature sensors attached to the various system components. These temperatures are correlated with a set of predetermined calibration parameters to correct the detector readings.
