AbstractWe present an update of the monitoring campaign we have undertaken to probe the most massive black holes in powerful quasars at high redshift through the reverberation mapping technique. Once this campaign has finished, we will be able to directly measure broad line region (BLR) sizes of quasars at z ~ 2−3, improving dramatically the BLR size-luminosity relation, and therefore, black hole mass estimates based on this relationship. So far, we have identified a dozen highly variable sources suitable for future cross-correlation analysis and reverberation measurements.