In thesis, the seismic analysis of two-storey office building in the area of Kamnik is performed. The building, which was designed in 1978 by using the then applicable rules for earthquake-resistant design of buildings, consisting of reinforced concrete frame and masonry infills. Basic articles of regulation valid in 1978 are firstly presented. Follow explanation of the Eurocodes with an emphasis on rules which address the consideration of the effects of masonry infills. In the second part of the thesis, the design seismic forces are calculated according to both standards, while in the case of Eurocode 8, the design seismic forces are assessed by using three different structural models. In addition to base case model, where beam cross sections were considered rectangular, the beam cross sections were modelled with consideration of the effective width of slab, firstly without consideration of the effect of masonry infill and secondly with consideration of infills, which were modelled by diagonals. All analyses were performed by ETABS and SAP2000. It was found that the design seismic forces according to the regulations from the time of the design of the facility were approximately three times smaller than the design seismic forces calculated according to Eurocodes. As a result, the amount of longitudinal reinforcement in the columns of the ground floor was around one-fifth of the required reinforcement according to Eurocodes, while in the top floor the amount of reinforcement in the columns was around one third of the required longitudinal reinforcement based on Eurocodes. The difference would be even greater if the design of the columns would account all the provisions of Eurocode 8. Consideration of infills in the structural model, decreased the vibration periods of the structure from 25% to 50% relative to the period obtained in the case of bare frame, but the design seismic forces for the case under consideration remained unchanged.