  The transmission grating spectrometers on AXAF have sufficient sensitivity
and energy resolution to detect resonance X-ray absorption lines in the spectra
of distant quasars. Such lines would be produced in an ionized, and somewhat
chemically enriched component of the inter-galactic medium. The bulk of the
baryonic content of the universe at redshifts <=2-3 could be in this form and
would thus be revealed by AXAF.
