  A 7.5 years spectrophotometric monitoring program of 28 Palomar-Green quasars
to determine the size of their broad emission line region (BLR) is reviewed. We
find both the continuum and the emission line fluxes of all quasars to vary
during this period. Seventeen objects has adequate sampling for reverberation
mapping and in all of them we find the Balmer line variations to lag those of
the continuum by ~100 days. This study increases the available luminosity range
for studying the size-mass-luminosity relations in active galactic nuclei
(AGNs) by two orders of magnitude and doubles the number of objects suitable
for such studies. Combining our results with data available for Seyfert 1
galaxies, we find the BLR size to scale with the rest-frame 5100 A luminosity
as L^{0.70 +/- 0.03}. This result is different from previous studies, and
suggests that the effective ionization parameter in AGNs may be a decreasing
function of luminosity. We are also able to constrain, subject to the
assumption that gravity dominates the motions of the BLR gas, the scaling
relation between the mass of the central black hole and the AGN's luminosity.
We find that the central mass scales with the 5100 A luminosity as
M\proptoL^{0.5 +/- 0.1}.
  A program to monitor 11 high-luminosity quasars is presented here for the
first time. Preliminary results from this program indicate continuum variation
of order of 0.1 mag in all objects. We illustrate the importance and
feasibility of monitoring those objects spectrophotometrically. When this
program will be completed reverberation mapping studies will cover the entire
AGNs luminosity range from 10^{41} to 10^{48} ergs/s.
