Biotrickling filters (BTFs) are often subjected to transient-state operation due to different variations in the operation of industrial-scale sources of pollution. In this research, performance of a laboratory-scale BTF packed with pall ring and pumice (1:1 v/v) and inoculated with Ralstonia eutropha was evaluated for the treatment of toluene vapor under various transient conditions. The experiments were performed at empty bed residence times (EBRTs) of 45 and 90 s and toluene inlet concentration in the range of 0.5-4 g m(-3). The transient-state experiments consisted of a sudden increase in inlet gas concentration, sudden change of trickling liquid rate, intermittent loading for 10 h day(-1), aeration without toluene loading during shutdown periods, and long-term starvation. The maximum elimination capacity (ECmax) was 280 g m(-3) h(-1) under continuous loading. The removal efficiency (RE) reached 90 % in intermittent loading experiments at toluene inlet concentration of 3 g m(-3) in less than 1 h after loading initiation. RE dropped to 50 % due to 4.5-fold increase in the inlet loading rate (ILR) during shock load experiment. The system became completely active after 24 h, when the BTF was subjected to a long-term starvation period for 7 days. The results showed that aeration at non-toluene loading periods could improve the BTF performance under intermittent loading condition.