  An enhancement for the $\eta$ production in proton-neutron collisions as
compared with that in proton-proton scattering has been recently observed. We
present a calculation for the production cross section, in proton-neutron
collisions near threshold, within instanton model for the QCD vacuum and show
that a specific flavor dependent nonperturbative quark-gluon interaction
related to instantons is able to explain the observed enhancement.
