The ventilation strategy, air distribution method and air change rate may affect building energy consumption significantly. However, this strategy is also related to contaminant dispersion, its removal efficiency and the risk of cross-infection in buildings. In this study, the effects of air distribution methods on aerosol particle behaviour in a ventilated room have been experimentally tested. Experiments were conducted in a full-scale test chamber with the source of contaminant (a nebulised solution of sodium chloride) positioned at the air supply and air exhaust sides. Displacement ventilation and mixing ventilation with one-way and four-way air supply through ceiling diffusers were tested at I, 2,3 and 4 air changes per hour. The concentration of particles was monitored within 10 min after the injection using six optical particle counters located in one plane section of the room. Aerosol particle decay was used for calculating the age of the air and analysing the ventilation efficiency. Computational fluid dynamics (CFD) predictions were performed to determine the spatial particle dispersion in the room and were compared to the results of the experiment. Experimental results showed that at lower air change rates, one-way mixing ventilation directed particles towards air exhaust diffusers more efficiently, while four-way mixing ventilation enabled more particles to remain airborne. At higher air exchange rates (3 and 4 ach), mixing ventilation with one-way air supply prevented aerosol particle transport to the opposite side of the room. The displacement air distribution appeared to be rather inefficient in the removal of particles from the chamber, which was reflected by the relatively high age of the air (of average 16.7 s at 3-4 ach) compared to the mixing ventilation (of average 9.9 s at 3-4 ach). (C) 2014 Elsevier B.V. All rights reserved.