Current microlensing searches calibrate the mass fraction of the Milky
Way halo that is in the form of massive astrophysical compact halo ob
jects (MACHOs). We show that surveys like the Sloan Digital Sky Survey
(SDSS) can probe the same quantity in halos of distant galaxies. Micr
olensing of background quasars by MACHOs in intervening galaxies would
distort the equivalent width distribution of the quasar emission line
s by an amplitude that depends on the projected quasar-galaxy separati
on. For a statistical sample of similar to 10(5) quasars as expected i
n the SDSS, this distortion is detectable at the greater than or simil
ar to 2 sigma level out to a quasar-galaxy impact parameter of several
tens of kpc, as long as extragalactic halos are made of MACHOs. Detec
tion of this signal would test whether the MACHO fraction inferred for
the Milky Way halo is typical of other galaxies.