The moon as light source has been used to measure trace gas concentrations in the infrared spectral region. The paper describes the measurement technique and the characteristics of the analysis. Below a wavenumber of 1500 cm-1 the atmospheric emission needs to be considered in the analysis. We have derived a simple correction factor which allows to use available solar absorption retrieval codes and correct the retrieved results for the effect of the atmospheric emission later on. Furthermore, the approach presented allows us to estimate the influence of the atmospheric emission on the results. Below 1500 cm-1 and in the polar regions the uncertainties of the simple correction method are within the uncertainties caused by the signal-to-noise ratio. At midlatitudes or in the tropics the atmospheric emission contribution increases to more than 50%. Spectra recorded above 2600 cm-1 show a negligible emission contribution, even in the tropics, and can be treated without considering the atmospheric emission. © 2002 Elsevier Science Ltd. All rights reserved.