  We study the role of hydrodynamic interactions for the relaxation of
segments' orientations in dendrimers. The dynamics is considered in the Zimm
framework. It is shown that inclusion of correlations between segments'
orientations plays a major role for the segments' mobility, that reveals itself
in the NMR relaxation functions. The enhancement of the reorientation dynamics
of segments due to the hydrodynamic interactions is more significant for the
inner segments. This effect is clearly pronounced in the reduced spectral
density $\omega J(\omega)$, whose maximum shifts to higher frequencies when the
hydrodynamic interactions are taken into account.
