  We test the recently published all-sky reddening map of Schlegel, Finkbeiner
& Davis (1998 [SFD]) using the extinction study of a region in the Taurus dark
cloud complex by Arce & Goodman (1999 [AG]). In their study, AG use four
different techniques to measure the amount and structure of the extinction
toward Taurus, and all four techniques agree very well. Thus we believe that
the AG results are a truthful representation of the extinction in the region
and can be used to test the reliability of the SFD reddening map. The results
of our test show that the SFD all-sky reddening map, which is based on data
from COBE/DIRBE and IRAS/ISSA, overestimates the reddening by a factor of 1.3
to 1.5 in regions of smooth extinction with A_V > 0.5 mag. In some regions of
steep extinction gradients the SFD map underestimates the reddening value,
probably due to its low spatial resolution. We expect that the astronomical
community will be using the SFD reddening map extensively. We offer this Letter
as a cautionary note about using the SFD map in regions of high extinction (A_V
> 0.5 mag), as it might not be giving accurate reddening values there.
