  We discuss the effects of the $s$-channel unitarization on the $x$ and
$Q^{2}$ dependence of structure functions. The unitarization is implemented at
the level of photoabsorption cross sections by resorting to the light--cone
wave functions of virtual photons and to the diagonalization property of the
scattering matrix in a basis of Fock states of the photon with fixed transverse
size. Triple pomeron effects are also explicitly taken into account. We find
large unitarity corrections to the structure functions at $x < 10^{-2}$. The
results are in very good agreement with the existing NMC and the preliminary
HERA data.
