The paper deals with the problems related to the structural design, construction and tests of a group of seismically isolated buildings, just constructed in Ancona for the SIP (Italian Telecommunications Company) Regional Administration Centre, which is the first Italian example of this technology. The Ancona region has been subjected to several earthquakes. The last one was recorded on 14 June 1972 showing a single shock-type wave with a peak acceleration of 0.53 g. The use of seismic isolation for the main buildings was very appealing because of its capability to assure adequate protection to the high-tech equipment and to the relevant valuable data under process. After a short review of the design requirements, the case history, covering the dynamic analysis, the structural design, also the construction and the full-scale tests is reported. A comparison between the costs of a conventional structure and of one with base isolation is also reported, showing a net saving of 7% for the latter. The paper deals extensively with the full-scale tests performed on one of the base isolated buildings. The assumptions of the structural design and of the isolation system were verified and the experimental results were recorded and analysed within a R&D program promoted by ENEA (Italian National Commission of Nuclear and Alternative Energy Sources) and ENEL (Italian National Utility) to constitute a reference for further applications to buildings and plants located in seismic zones.