  We present preliminary results from a reverberation mapping program to
measure the Broad Line Region size in high-redshift, high-luminosity quasars.
The observations are carried out at the Hobby-Eberly Telescope and at the Wise
Observatory. The data cover 8 yr of photometric monitoring of 11 quasars, and
2.5 yr of spectrophotometric monitoring of 7 of these sources. Thus far we
detected continuum variations but no line variations. We find that the continua
of the high-luminosity quasars have smaller variability amplitudes and longer
variability timescales compared with low-luminosity AGNs.
