For large bulk disordered media, light transport is generally successfully described by a diffusion process. This picture assumes that any interference is washed out under configuration average. However, it is now known that, under certain circumstances, some interference effects survive the disorder average and in turn lead to wave localizations effects. In this paper, we investigate coherence of a monochromatic laser light propagating in an optically thick sample of laser-cooled strontium atoms. For this purpose, we use the coherent backscattering effect as an interferometric tool. At low laser probe beam intensities, phase coherence is fully preserved and the interference contrast is maximal. At higher intensities, saturation effects start to set in and the interference contrast is reduced.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.