The task of this work is to investigate the influence of the deflections of the vertical on geodetic networks used for the construction of major buildings and infrastructures such as tunnels and bridges in the area of Sarajevo. In contrast to distance measurements, directions and zenith angles are influenced by the gravity field. Therefore, for the highest accuracy requirements, it may be necessary to consider the impact of local deflections of the vertical. Until now there is available only sparse information about the deflection field in the vicinity of Sarajevo. In this context 105 test points (2-3 km point distance), arranged in profiles, were selected where the terrain correction has been calculated through various methods, i.e., the prism method and the Fast Fourier Transformation. The calculations were carried out by an upgraded version of the Fortran program LOTAB, developed at the Institute of Geodesy and Geophysics of the Vienna University of Technology. From the horizontal components of the terrain correction the deflections of the vertical were derived. The location and length of the chosen profiles resulted from the introduced influence zone (reduction radius) of 30km and is dictated by the small size of the available terrain grid (resolution 50m x 50m). First of all, with the help of simulations, the overall influence of the deflections of the vertical on geodetic measurements in different azimuths and zenith angles is investigated. Methodically the surveyor can quickly and easily decide by means of a provided graphical representation if for a given coordinate accuracy to be accomplished the local deflection of the vertical has to be taken into account. Later on the above mentioned calculated deflections were applied to a test network of 250 GPS stations with an average distance of 1km around Sarajevo which was further densified by polygon lines measured with total stations.