Toluene vapour was degraded in a biofilter packed with various initial moisture contents of packing materials at 650-1000 mg (toluene)/m(3) (gas) and 24.0-36.8 g/m(3)/h load. The results demonstrated that a higher degradation capacity (DC) could be reached within a shorter operation time at a higher initial moisture content. During 144 h operation, the maximal degradation rate (DR) and degradation capacity (DC) were, respectively, 60%, 20 g/m(3)/h for 30 and 40% initial moisture content. For 60 and 70% initial moisture content, the DR and DC could be higher at the beginning of operation, which were above 70% and 20 g/m(3)/h, and reached the maximum of 100% and above 25-30 g/m(3)/h at about 75 h operation. The microbial determination results of packing materials (30, 50 and 70% initial moisture content) in biofilter operating for 144 It showed that the initial moisture content of packing materials would affect the numbers and types of microbial community of packing materials. With the increase in the initial moisture content, the quantity of moulds and actinomyces would decrease and the number of bacteria would increase. The packing material with 50% initial moisture content was beneficial to the yeast growth. (C) 2002 Elsevier Science Ltd. All rights reserved.