ABSTRACT—A botanically based biofilter integrated directly into the air handling system of an indoor space removed significant amounts of VOCs present in parts per billion by volume concentrations. For toluene, ethylbenzene and o-xylene, the greatest removal per pass (removal efficiency) was at the slowest influent flux (ca 0.02 m s-1), however the greatest removal per unit time and biofilter volume (elimination capacity) was at the more rapid fluxes (ca 0.1 to 0.2 m s-1). Cooler temperatures allowed greater partitioning of the VOCs into the water column which had a greater impact on removal than its reduction in microbial activity. The halogenated compound PCE, was removed from the air stream but there was little evidence of degradation.