  86 GHz Very Long Baseline Polarimetry probes magnetic field structures within
the cores of Active Galactic Nuclei at higher angular resolutions and a
spectral octave higher than previously achievable. Observations of 3C273 and
3C279 taken in April 2000 with the Coordinated Millimeter VLBI Array have
resulted in the first total intensity (Stokes I) and linear polarization VLBI
images reported of any source at 86 GHz. These results reveal the 86 GHz
electric vector position angles within the jets of 3C273 and 3C279 to be
orthogonal to each other, and the core of 3C273 to be unpolarized. If this lack
of polarization is due to Faraday depolarization alone, the dispersion in
rotation measure is >=90000 rad/m^2 for the core of 3C273.
