  We investigate the Reidemeister spectrum of direct products of nilpotent
groups. More specifically, we prove that the Reidemeister spectra of the
individual factors yield complete information for the Reidemeister spectrum of
the direct product if all groups are finitely generated torsion-free nilpotent
and have a directly indecomposable rational Malcev completion. We show this by
determining the complete automorphism group of the direct product.
