  So far the masses of about 50 active galactic nuclei have been measured
through the reverberation mapping technique (RM). Most measurements have been
performed for objects of moderate luminosity and redshift, based on H$\beta$,
which is also used to calibrate the scaling relation which allows single-epoch
(SE) mass determination based on AGN luminosity and the width of different
emission lines. The SE mass obtained from CIV$(1549 {\rm\AA})$ line shows a
large spread around mean values, due to complex structure and gas dynamics of
the relevant emission region. Direct RM measures of CIV exist for only 6 AGNs
of low luminosity and redshift, and only one luminous quasar (Kaspi et al
2007). We have collected since 2003 photometric and spectroscopic observations
of PG1247+267, the most luminous quasar ever analyzed for RM. We provide light
curves for the continuum and for CIV$(1549 {\rm\AA})$ and
CIII]$(1909{\rm\AA})$, and measures of the reverberation time lags based on the
SPEAR method (Zu et al. 2011). The sizes of the line emission regions are in a
ratio $R_{CIII]}/R_{CIV}\sim 2$, similar to the case of Seyfert galaxies,
indicating for the first time a similar ionization stratification in a luminous
quasar and low luminosity nuclei. Due to relatively small broad line region
size and relatively narrow line widths, we estimate a small mass and an
anomalously high Eddington ratio. We discuss the possibility that either the
shape of the emission region or an amplification of the luminosity caused by
gravitational lensing may be in part responsible of the result.
