Within the displacement ventilation (DV) field, this paper presents an experimental study of thermal stratification in a ventilated room in which there is a heat source. The ventilation system maintains plume development up to a limiting height, above which the air stream is mixed. Temperature stratification arises within the test room. Its interface is of significant thickness and its position is identified by that of the maximum standard deviation of temperature fluctuations. The change in the height of this interface is studied under different experimental conditions. Results confirm the laws already obtained for zones close to and far away from the source and they also allow a law governing the transition between these two zones to be proposed. (c) 2005 Elsevier Ltd. All rights reserved.