  We present a discussion of the effects induced by the bulk viscosity on the
very early Universe stability. The matter filling the cosmological (isotropic
and homogeneous) background is described by a viscous fluid having an
ultrarelativistic equation of state and whose viscosity coefficient is related
to the energy density via a power-law of the form $\zeta=\zeta_0 \rho^\nu$. The
analytic expression of the density contrast (obtained for $\nu=1/2$) shows
that, for small values of the constant $\zeta_0$, its behavior is not
significantly different from the non-viscous one derived by E.M. Lifshitz. But
as soon as $\zeta_0$ overcomes a critical value, the growth of the density
contrast is suppressed forward in time by the viscosity and the stability of
the Universe is favored in the expanding picture. On the other hand, in such a
regime, the asymptotic approach to the initial singularity (taken at $t=0$) is
deeply modified by the apparency of significant viscosity in the primordial
thermal bath i.e. the isotropic and homogeneous Universe admits an unstable
collapsing picture. In our model this feature regards also scalar perturbations
while in the non-viscous case it appears only for tensor modes.
