Abstract The Mars-Express mission in 2003 will carry the Planetary Fourier Spectrometer (PFS) for measurement of infrared radiation emitted by the atmosphere and surface. The retrieval of vertical temperature profiles is based on an iterative comparison of measured and simulated spectra in the 15 μm CO 2 band. A sensitivity study is performed to define the required accuracy of line-by-line CO 2 transmittance simulations to obtain reliable temperature results. The influence of instrumental noise on the temperature retrieval is also discussed. Synthetic measurements as well as selected spectra from the Mariner 9-IRIS data were used in the study.