  The Pierre Auger Observatory has been collecting data in a stable manner
since January 2004. We present here a study of the cosmic ray composition using
events recorded in hybrid mode during the first years of data taking. These are
air showers observed by the fluorescence detector as well as the surface
detector, so the depth of shower maximum, Xmax, is measured directly. The
cosmic ray composition is studied in different energy ranges by comparing the
observed average Xmax with predictions from air shower simulations for
different nuclei. The change of <Xmax> with energy (elongation rate) is used to
derive estimates of the change in primary composition.
