IASI, the Infrared Atmospheric Sounding Interferometer is a key payload element of the METOP series of European meteorological polar-orbit satellites. By measuring the thermal infrared radiation emitted by the earth and its atmosphere in 8461 spectral channels, this instrument provides information on the atmospheric temperature and chemical composition. In this poster, we show the first results of 3D (possibly 4D) variational assimilation experiments of clear IASI radiances, demonstrating the impact of this new instrument on the Canadian Meteorological Center forecasts.