Thermal comfort and air quality were studied in three multi-family buildings located in urban environments. Measurements of air velocities close to the supply devices are presented along with measurements of CO, TVOC, NO and N02. In addition, particle measurements were carried out to check the filter efficiency in one of the buildings (Sl) which is specially designed for people with allergy problems. The total air change rate for this building is higher than for normal residential buildings and three different types of air filter are installed in the ventilation system. The results of the thermal comfort measurements in the buildings vary considerably. For two of the buildings thermal comfort can be regarded as acceptable, but can be further improved. The selection and location of the air inlet devices in the third building are not acceptable. The monitoring of the contaminants outdoors and indoors was carried out for diurnal periods. The measured contaminants outside building 51 show good correlation between each other, and the concentrations of gases and particles were considerably lower in the supply air than in the outdoor air outside the apartment where the measurements were made. The importance of not taking samples over too short a period of time is also shown.