  We present broad band imaging observations obtained with the ``peak up''
imagers of the Spitzer Space Telescope Infrared Spectrograph (IRS) at
wavelengths of 16micron and 22micron for a number of sources detected primarily
at submillimeter wavelengths, which are believed to be at high, though
undetermined, redshift. We targeted 11 sources originally detected by SCUBA and
5 submillimeter sources detected at 1.2mm by MAMBO. Two optically discovered
quasars with z>6 were also observed to determine if there is detectable dust
emission at such high redshifts. Seven of the submillimeter sources and both
high-redshift quasars were detected, and upper limits of about ~50microJy apply
to the remainder. Using their mid-/far-IR colors, we demonstrate that all of
the submillimeter sources are at z>1.4. The mid-IR colors for two of our
detections and three of our strong upper limits suggest that these galaxies
must be at z>2.5. We also introduce a technique for estimating redshifts and
source characteristics based only on the ratio of fluxes in the 16micron and
22micron images.
