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 ~ { } \pm~ { } 0.29 ) ~ { } \mathrm { pc } , which is in excellent agreement with the previous Hipparcos result .