Biodegradation of toluene vapour was investigated for 168 days in a polyurethane packed biofilter inoculated with a mixed microbial population. Biofilter consisted of five square cross-section modular units each of size 0.16 m x 0.16 m x 0.20 m and filled with the polyurethane foam cubes up to a height of 0.15 m. Inlet concentration of toluene was varied from 0.04 to 2.5 gm(-3) and the volumetric flow rate of toluene loaded air from 0.06 to 0.90 m(3) h(-1). Depending upon initial loading rates, removal efficiency ranging from 68.2 to 99.9% and elimination capacity ranging from 10.85 to 90.48 g h(-1) m(-3) were observed during steady state operations. More than 90% removal efficiency was observed up to an inlet loading rate of 76.3 g h(-1) m(-3). High carbon recovery (>90%) indicated effective biodegradation in the bed. Low variation of pH (7.2-8.8) and pressure drop (45.8-76.3 Pa) was observed. The stability of the biomass was evident from the fast response of the biofilter to shutdown and restartup. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.