This paper reports the results of a numerical study on removal of two contaminants from a three-dimensional enclosure with one inlet, one exhausting port and one returning port. In the formation of the problem, use is made of Reynolds stress model (RSM). The governing equations are solved by means of the SIMPLE algorithm. Lots of cases have been studied for the sensitivity analysis, including more practical cases from the total fresh air supplying to the total recirculation situations. The influence of inlet velocity, fresh air ratio, recirculating air filtered removal efficiency and contaminant property is investigated. The indoor contaminant is studied parametrically as a function of governing dimensionless numbers (Reynolds number and Schmidt number). The results show the above parameters have complex influence to indoor contaminant removal. (C) 2007 Elsevier Ltd. All rights reserved.