  A possible application of the evolution equation for the truncated Mellin
moments to determination of the parton distributions in the nucleon is
presented. We find that the reconstruction of the initial parton densities at
scale $Q_0^2$ from their truncated moments at a given scale $Q^2$ is exact and
unique for small number of free parameters ($\leq 3$), even for the limited
$x$-region of experimental data. For larger number of adjustable parameters the
obtained fits are not unique and one needs an additional knowledge of the
small-$x$ behaviour of the parton densities to make the reconstruction
procedure reliable. We apply successfully our method to HERMES and COMPASS
spin-dependent valence quark data.
