This paper presents results and observations from a long-term pilot test of bulk media biofilters to assess their reduction of odors and volatile organic compounds (VOCs). The pilot biofilter was built in four modules to enable testing of different media mixes. The media components included graded bark, topsoil, compost, peat moss, and oyster shells. Moisture was added by two methods, inlet air humidification and surface sprinklers. Bench-scale column tests were performed in advance to determine pressure drops through, and compaction of, various media. Performance of the biofilter was measured in terms of its reduction of the following contaminants: hydrogen sulfide, ammonia, and amine; odor units; and VOCs. Three foul air sources were used with varying contaminant concentrations. Table I shows the average reduction through the biofilter of odorous compounds and several VOCs.