  The pre-Galactic abundance of lithium offers a unique window into non-thermal
cosmological processes. The primordial Li abundance is guaranteed to be present
and probes big bang nucleosynthesis (BBN), while an additional Li component is
likely to have been produced by cosmic rays accelerated in large scale
structure formation. Pre-Galactic Li currently can only be observed in low
metallicity Galactic halo stars, but abundance measurements are plagued with
systematic uncertainties due to modeling of stellar atmospheres and convection.
We propose a new site for measuring pre-Galactic Li: low-metallicity,
high-velocity clouds (HVCs) which are likely to be extragalactic gas accreted
onto the Milky Way, and which already have been found to have deuterium
abundances consistent with primordial. A Li observation in such an HVC would
provide the first extragalactic Li measurement, and could shed new light on the
apparent discrepancy between BBN predictions and halo star Li abundance
determinations. Furthermore, HVC Li could at the same time test for the
presence of non-primordial Li due to cosmic rays. The observability of
elemental and isotopic Li abundances is discussed, and candidate sites
identified.
