  Three eclipsing binary systems with astrometric orbit have been studied. For
a detailed analysis two circular-orbit binaries (VW Cep and HT Vir) and one
binary with an eccentric orbit (zeta Phe) have been chosen. Merging together
astrometry and the analysis of the times of minima, one is able to describe the
orbit of such a system completely. The O-C diagrams and the astrometric orbits
of the third bodies were analysed simultaneously for these three systems by the
least-squares method. The introduced algorithm is useful and powerful, but also
time consuming, due to many parameters which one is trying to derive. The new
orbits for the third bodies in these systems were found with periods 30, 221,
and 261 yr, and eccentricities 0.63, 0.37, and 0.64 for VW Cep, zeta Phe, and
HT Vir, respectively. Also an independent approach to compute the distances to
these systems was used. The use of this algorithm to VW Cep gave the distance
d=(27.90 +/- 0.29) pc, which is in excellent agreement with the previous
Hipparcos result.
