According to previous literature works on biofiltration of mixtures of aromatic compounds vapors, xylene is the most resistant to biodegradation in biofilters. However, only limited information is available about the application of biofiltration to the removal of xylene vapors as the sole contaminant in the air stream. In the present work biofiltration of xylene vapors has been investigated on a laboratory scale biofilter packed with a new filter material composed essentially of peat mixed with structuring and conditioning agents and initially inoculated with a microbial consortium. Three various gas flow rates, i.e. 0.4, 0.7 and 1 m(3) h(-1), were tested for xylene inlet concentration ranging from 0.2 to 4 g m(-3). The biofilter proved to be highly efficient in the removal of xylene at a gas flow rate of 0.4 m3 h(-1) corresponding to a gas residence time of 157 s. For all the tested inlet concentrations, both the removal efficiency and the elimination capacity decreased for high gas flow rates. For all the tested gas flow rates, a decrease in the elimination capacity was noticed for high xylene inlet concentration. The follow-up of carbon dioxide concentration profile through the biofilter revealed that the mass ratio of carbon dioxide produced to the xylene removed was approximately 2.5/1, which confirms complete degradation of xylene if one considers the fraction of the consumed organic carbon used for the microbial growth. (C) 2000 Elsevier Science S.A. All rights reserved.