Indirect linking of the Hipparcos catalogue to extragalactic reference frame via earth orientation parameters Jan Vondrak, Astronomical Institute Prague, Czech Republic The indirect method of linking the Hipparcos reference frame to the frame defined by extragalactic radio sources is described. To this end, two independent time series of the Earth orientation parameters observed by two different techniques with respect to the two reference frames are used: a) Optical Astrometry observations (referred to Hipparcos stars) , b) VLBI observations (referred to extragalactic ob- jects). The parallel use of both techniques during the last decade enables to determine both orientation of the two reference frames at a fixed epoch and their mutual slow rotation, with precision of at least 1mas and 1mas/year, respectively. The potentiality of the method will be demonstrated on the example based on the star catalogues origi- nally used at the participating observatories, brought into a common reference frame by means of Hipparcos Input Catalogue.