  For microlensing case angular distances between images or typical astrometric
shifts due to microlensing are about $10^{-5}-10^{-6} \mu as$. Such an angular
resolution will be reached with the space space--ground interferometer
Radioastron. The basic targets for microlensing searches should be bright
point-like radio sources at cosmological distances. In this case, an analysis
of their variability and a solid determination of microlensing could lead to an
estimation of their cosmological mass density, moreover, in this case one could
not exclude a possibility that non-baryonic dark matter also form microlenses
if the corresponding optical depth will be high enough. To search for
microlensing the most perspective objects are gravitational lensed systems as
usually, like CLASS gravitational lens B1600+434, for instance. However, for
direct resolving these images and direct detection of apparent motion of the
knots, a Radioastron sensitivity have to be improved, since an estimated flux
density is too low and to observe the phenomena one should improve sensitivity
in 10 times at 6 cm wavelength, for instance, otherwise, it is necessary to
increase an integration time (assuming that a radio source has a typical core
-- jet structure and microlensing phenomenon is caused superluminal apparent
motion of knots). Therefore, a launch of space interferometer Radioastron will
give new excellent facilities to investigate microlensing in radio band, since
in this case there is a possibility not only to resolve microimages but also
observe astrometric microlensing.
