Air temperature, air humidity and ventilation has been measured in a Swedish baroque castle. Results are presented for a measurement campaign comprising four periods under various climatic conditions. A passive tracer gas method, known as the homogeneous emission technique has been used to measure the ventilation rates and air distribution in the building. As the palace is essentially unheated, wind pressure is the main driving force for ventilation. The air change rate is highly varying and differs considerably in different parts of the building (0.5 1.5 ACH). The results of window renovation in certain rooms indicates that adding inner windows seems to be a possibly means to reduce infiltration rate and stabilize the indoor climate. Other means of retrofitting are also discussed.