  We study the nucleon-nucleon interaction in the isoscalar-scalar channel
using t he chiral unitary approach. The $t$-matrix of the pion-pion scattering
in this c hannel is summed up to all orders using the B-S equation. We find
that the calcu lated results at long distances are close to those of the
$\sigma$-exchange inte raction. In addition, there appears a shorter range
repulsion in this channel.
