  The physics case for a possible fixed target polarized nucleon-nucleon
collision experiment at HERA is described. The experiment named HERA-N could be
realized using an internal polarized gas target in the HERA
polarized/unpolarized proton beam. A wide spectrum of nucleon spin structure
problems could be investigated and the experiment would constitute a fixed
target complement to the RHIC spin physics program with competitive statistical
accuracy.
