  We study the contamination of the B-mode of the Cosmic Microwave Background
Polarization (CMBP) by Galactic synchrotron in the lowest emission regions of
the sky. The 22.8-GHz polarization map of the 3-years WMAP data release is used
to identify and analyse such regions. Two areas are selected with
signal-to-noise ratio S/N<2 and S/N<3, covering ~16% and ~26% fraction of the
sky, respectively. The polarization power spectra of these two areas are
dominated by the sky signal on large angular scales (multipoles l < 15), while
the noise prevails on degree scales. Angular extrapolations show that the
synchrotron emission competes with the CMBP B-mode signal for tensor-to-scalar
perturbation power ratio $T/S = 10^{-3}$ -- $10^{-2}$ at 70-GHz in the 16%
lowest emission sky (S/N<2 area). These values worsen by a factor ~5 in the
S/N<3 region. The novelty is that our estimates regard the whole lowest
emission regions and outline a contamination better than that of the whole high
Galactic latitude sky found by the WMAP team (T/S>0.3). Such regions allow $T/S
\sim 10^{-3}$ to be measured directly which approximately corresponds to the
limit imposed by using a sky coverage of 15%. This opens interesting
perspectives to investigate the inflationary model space in lowest emission
regions.
