1 Introduction A new development in indoor climate control is Thermally Activated Building Systems (TABS). This system uses building mass to heat and cool the building. Water filled pipes are embedded in the core of the concrete slab. Water near comfort temperature is used. Slow accumulation of concrete results in small adaptation possibilities in order to meet the needs of users. Research has shown that the storage capacity of the concrete is in principal more than enough to maintain comfortable room temperature. The objective of the research is examining thermal comfort where obtained with TABS. Measurements were done in one office and three schools. 2 Contibution to the conference In 4 different buildings with TABS measurements were done and questionnaires held. These 4 buildings were 3 schools and one city hall. In the city hall 2 rooms were examined and in the schools one classroom. During one week all the relevant parameters to calculate the PMV values were determined. In the same period the questionares were held. 3 Results Users opinion is the central point of this research. First of all, perception of indoor climate is important for determining whether users are comfortable. Secondly it is important how the interaction with the system is experienced. Users of all measured rooms have filled in a questionnaire. Respectively temperature, stability of temperature and air speed was rated.