Abstract: The invention relates to an apparatus and a method for improved correction of drift in an infrared measuring instrument. The measurement signal furnished by a thermal detector is split into a direct voltage component and an alternating voltage component. By means of calibration curves (24, 27), a calculated comparison variable T DC , korr 900 is formed from a measured, averaged concentration value c AC1 900 . The correction value ?T for the drift correction is obtained from the difference between the corresponding measured size of the direct voltage component T DC 900 and the comparison variable T DC , korr 900 .