We discuss the experimental indications on the behaviour of F_2(x,Q^2) at
small x both in proton and nuclear targets. By comparing the parametrizations
of the data we conclude that shadowing correction effects in a proton target
can appear at a noticeable level for x=(2 - 4)\times10^{-4} and Q^2\sim 10^1
GeV^2, namely inside the HERA regime.Comment: 5 pages, Latex, no figure
