  Shell effects in nuclei close to the neutron-drip lines have been
investigated. It has been demonstrated in the relativistic mean-field theory
that nuclei very far from stability manifest the shell effects strongly. This
behaviour is in accord with the predictions of nuclear masses in the
finite-range droplet model including shell corrections. As a consequence we
find a large neutron halo in nuclei near the neutron-drip line. The shell
effects predicted in the existing Skyrme mean-field theory in comparison are
significantly weaker than those of the other approaches.
