Pellet injection is expected to be used to raise and control the density in a reactorgrade plasma. The viability and the efficiency of this method need to be investigated in large tokamaks in order to gain confidence in extrapolation to ITER. The JET pellet system, which already included a centrifuge injector, has recently been upgraded with a new High Frequency pellet injector (HFPI) designed to deliver pellets both for fuelling purposes and for ELM pacing. The new HFPI system has been successfully used in the fuelling mode (design mass range 2.2-3.8¥1021 D atoms), delivering pellet trains (~30) through the Low Field Side track (LFS) which reached the plasma with mass losses of about 40% up to a speed of 200m/s and a repetition rate up to 10Hz. Due to technical problems, the Vertical High Field Side line (VHFS) has not been fully exploited while the High Field Side one (HFS) is still to be tested. Since the last pellet experiments at JET, new diagnostics, including a fast visible camera, high resolution Thomson scattering and polarimetry, have become fully operational thus improving the accuracy of the analysis.