The amount and properties of high-redshift galactic and intergalactic (IG)
dust are largely unknown but could be investigated using multiwavelength ph
otometry of high-z objects that have a known intrinsic spectrum. Observatio
ns of gamma -ray burst (GRB) afterglows appear to support the theoretical m
odel of an adiabatic blast wave expanding into an external medium. In this
model the synchrotron peak flux is independent of frequency, providing a fl
at spectrum when observed over time, and therefore allowing straightforward
measurement of the relative attenuation of afterglow flux in widely separa
ted bands. Applying this method to dust extinction, we show that for a samp
le of afterglows that have been corrected by galactic extinction comparison
between the number counts of peak fluxes in X-ray versus optical can provi
de constraints on an intergalactic component of dust. A similar technique c
an probe the redshift dependence of extinction in GRB-forming regions witho
ut requiring an assumed relation between extinction and reddening by the du
st. Probing systematic changes in extinction with redshift, particularly in
IG and/or nonreddening dust, is crucial to a proper interpretation of the
Type Ia supernova Hubble diagram and similar observations and useful for un
derstanding GRB progenitor environments.