The concatenative real-time sound synthesis system CataRT plays grains from a large corpus of segmented and descriptor-analysed sounds according to proximity to a target position in the descriptor space. This can be seen as a content-based extension to granular synthesis providing direct access to specific sound characteristics. CataRT is implemented in Max/MSP using the FTM library and an SQL database. Segmentation and MPEG-7 descriptors are loaded from SDIF files or generated on-the-fly. CataRT allows to explore the corpus interactively or via a target sequencer, to resynthesise an audio file or live input with the source sounds, or to experiment with expressive speech synthesis and gestural control.