The paper presents results from the numerical modelling of the flow field in an existing ventilated office room. The numerical procedure is based on the 3D Reynolds equations closed by the k-e turbulence model and an equation for temperature solved by the finite volume method. The boundary conditions are set in accordance to detailed measurements of the velocity distribution in the air supply diffuser. The established complex flow conditions in the room, which are due to the presence of furniture and buoyancy forces, are presented. Field measurements were carried out for the particular investigation. An analysis is made of the temperature field based on a comparison between the experimental and numerical results. Conclusions are drawn about the organisation of ventilation in the investigated room.