  Using the 100-m Green Bank Telescope, we have conducted a cm-wavelength
search for CO J=1-0 line emission towards the high-redshift, far-infrared
luminous object, HDF850.1 over the redshift interval 3.3<z<5.4. Despite the
wealth of existing multi-wavelength observations, and the recent identification
of a galaxy counterpart in deep K' band (2.2 um) imaging, an unambiguous
spectroscopic redshift has not yet been obtained for this object. A
far-infrared-to-radio wavelength photometric redshift technique however,
predicts a ~90% probability that the redshift is in the range, 3.3<z<5.4
(equivalent to an observed redshifted CO J=1-0 emission line frequency,
26.5>nu(obs)>18.0 GHz), making HDF850.1 a potential occupent of the
`high-redshift tail' of submm selected galaxies. We have also conducted a
search for CO J=2-1 line emission over the narrower redshift range, 3.9<z<4.3.
although we do not detect any CO line emission in this object, our limits to
the CO line luminosity are in broad agreement with the median value measured in
the current sample of high-redshift, submm selected objects detected in high-J
CO line emission, but not sufficient to fully test the validity of the
photometric redshift technique.
