  High-accuracy astrometry permits the determination of not only stellar
tangential motion, but also the component along the line-of-sight. Such
non-spectroscopic (i.e. astrometric) radial velocities are independent of
stellar atmospheric dynamics, spectral complexity and variability, as well as
of gravitational redshift. Three methods are analysed: (1) changing annual
parallax, (2) changing proper motion and (3) changing angular extent of a
moving group of stars. All three have significant potential in planned
astrometric projects. Current accuracies are still inadequate for the first
method, while the second is marginally feasible and is here applied to 16
stars. The third method reaches high accuracy (<1 km/s) already with present
data, although for some clusters an accuracy limit is set by uncertainties in
the cluster expansion rate.
