Biofiltration is an aerobic degradation process in which a well-humidified contaminated air stream is passed through a porous packed medium that supports a thriving population of microbes. The removal of benzene vapor was investigated in a laboratory-scale biofilter packed with compost, inoculated with a mixed microbial consortium. This biofilter was operated continuously in six different phases for a period of 8 months at different flow rates, 0.024-0.144 m3 h-1 with benzene concentrations ranging up to 1.7 g m-3. Under steady-state conditions, the removal efficiencies (REs) in the biofilter was consistently greater than 78% when benzene loading was less than 20 g m-3 h-1. The maximum elimination capacity (EC) achieved in this study is 64 g m-3 h-1 at an inlet loading rate of 128 g m-3 h-1. The response of the biofilter to shutdown, restart operations and fluctuations in inlet con-centration, and flow rate was determined by subjecting the biofilter to inlet loads of up to 120 g m-3 h-1. The biofilter responded effectively to these loading conditions and was found to recover rapidly. The results from this study suggest that a compost biofilter is effective in treating benzene vapor under steady- and transient-conditions. © Springer-Verlag 2009.