  New calculations of the Galactic contamination over microwave background
radiation anisotropies are carried out. On one hand, when a frequency-dependent
contrast of molecular clouds with respect to the Galactic background of the
diffuse interstellar medium is taken into account, the anisotropic amplitude
produced by Galactic dust is increased with respect to previous calculations
and this is of the same order as that of the data from the observations. On the
other hand, if we take into account rotational dust emission, for instance, a
frequency independence of anisotropies in the microwave range may be obtained.
  This leads to the possibility that under some particular, but not impossible,
conditions all the microwave background radiation anisotropies may be due to
Galactic foregrounds rather than cosmological in origin. Moreover, a suspected
coincidence between the typical angular sizes of the microwave background
radiation anisotropies and those of nearby molecular clouds makes more
plausible the hypothesis of a purely Galactic origin for these anisotropies. It
is also argued that the correlation among structures at different frequencies,
the comparison of the power spectrum at different frequencies and the galactic
latitude dependence of the anisotropies are not yet proofs in favour of either
a cosmological or Galactic origin.
