  We repeat and extend the analysis of Eriksen et al 2004 and Hansen et al 2004
testing the isotropy of the Cosmic Microwave Background (CMB) fluctuations. We
find that the hemispherical power asymmetry previously reported for the largest
scales l=2-40 extend to much smaller scales. In fact, for the full multipole
range l=2-600, significantly more power is found in the hemisphere centered at
(theta=107 deg., phi=226 deg.) in galactic co-latitude and longitude than in
the opposite hemisphere consistent with the previously detected direction of
asymmetry for l=2-40. We adopt a model selection test where the direction and
amplitude of asymmetry as well as the multipole range are free parameters. A
model with an asymmetric distribution of power for l=2-600 is found to be
preferred over the isotropic model at the 0.4% significance level taking into
account the additional parameters required to describe it. A similar direction
of asymmetry is found independently in all six subranges of 100 multipoles
between l=2-600 and none of our 9800 isotropic simulated maps show a similarly
consistent direction of asymmetry over such a large multipole range. No known
systematic effects or foregrounds are found to be able to explain the
asymmetry.
