We measure the broad emission line region ( BLR ) size of a luminous , L \sim 10 ^ { 47 } { erg s ^ { -1 } } , high- z quasar using broadband photometric reverberation mapping .
To this end , we analyze \sim 7.5 years of photometric data for MACHO 13.6805.324 ( z \simeq 1.72 ) in the B and R MACHO bands and find a time delay of 180 \pm 40 days in the rest frame of the object .
Given the spectral-variability properties of high- z quasars , we associate this lag with the rest-UV iron emission blends .
Our findings are consistent with a simple extrapolation of the BLR size-luminosity relation in local active galactic nuclei to the more luminous , high- z quasar population .
Long-term spectroscopic monitoring of MACHO 13.6805.324 may be able to directly measure the line-to-continuum time-delay and test our findings .