The rate of biofiltration of 1, 5, 13, 40 or 100 mg MEK/m(3), through a 0.5-3.0 mm pine-tree bark bed, column height 0.25 or 0.45 m, phi0.175 m, contact time range 2.17-19.45 s, was approx. directly related to bed charge and to MEK wt. concn. at inlet to biofilter. As the time of bed operation was increased, bed performance fell to attain a value corresponding to a quasi steady state. As the MEK contact time was protracted while the MEK concn. at inlet was kept fixed, bed performance rose. As the MEK concn. before column was increased, the rate of biodegradation rose.