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 \sim 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 Å luminosity as L ^ { 0.70 \pm 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 Å luminosity as M \propto L ^ { 0.5 \pm 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 ^ { -1 } .