The invention relates to a method and an apparatus for non-dispersive analysis of gas mixtures for determining the concentration of such a first gas component in a gas mixture, whose absorbance may be influenced by other gas components of said gas mixture. The apparatus comprises a sample chamber (2) for containing the gas mixture, a radiation source (1) for transmitting radiation through the gas mixture, a first optical transmission band filter (5) with a first absorption transmission band of the first gas and a first radiation detector (4). The apparatus further comprises a second optical transmission band filter (8) with a second transmission band, which is outside the first transmission band, and a second detector (7). The concentration determining means (23) are arranged to determine the concentration of the first gas using a certain formula or formulas and using the detected intensities. The second transmission band is substantially or entirely outside the absorption bands of said first gas component and comprises a second absorption band of a certain gas component causing a distortion in the absorption band of the first gas component, the strength of the second absorption band being substantially less than the strength of the first absorption band.