Recent thermal conductivity measurements on UPt3 single crystals by Lu
ssier et al. indicate the existence of a strong b-c anisotropy in the
superconducting state. We calculate the thermal conductivity in variou
s unconventional candidate states appropriate for the UPt3 ''B phase''
and compare with experiment, specifically the E(2u) and E(1g) (1,i) s
tates predicted in some Ginzburg-Landau analyses of the phase diagram.
For the simplest realizations of these states over spherical or ellip
soidal Fermi surfaces, the normalized E(2u) conductivity is found, sur
prisingly, to be completely isotropic. We discuss the effects of inela
stic scattering and realistic Fermi surface anisotropy, and deduce con
straints on the symmetry class of the UPt3 ground state.