Treats investigations in office building where 1) flow rates of supply air, return air and ventilation between main office area and adjacent rooms were measured with an anemometer. Return air rates remained constant but ventilation rates varied widely during measurement periods. 2) CO2 was used as tracer gas to determine ventilation rates in offices. Calculates alterations in gas concentrations in rooms adjacent to stairwell and changes in outdoor air concentrations. During air conditioning, ventilation rates in the room were 4-5 room air changer per hour. Without air conditioning, air change rates were 1-2 per hour approximately.