The work reported here describes the aerobic biodegradation of reduced sulfur compound mixtures in air streams by biofilters. Rates of removal of hydrogen sulfide as a sole substrate and in the presence of organo-sulfur compounds were determined to see if there were any inhibitory effects of the organo-sulfur compounds on the rate of hydrogen sulfide removal. Experiments were conducted in three bench-scale biofilters packed with the mixtures of compost/perlite (4:1), hog fuel/perlite (4:1), and compost/hog fuel/perlite (2:2:1), respectively. Hydrogen sulfide, the predominant odorous gas produced from kraft pulping processes, was used as the main pollutant (substrate). Other organo-sulfur species (dimethyl sulfide and dimethyl disulfide), also emitted from kraft pulp mills, were used as competing (secondary) substrates in the waste gas stream. To describe rates of removal a Michaelis-Menten type kinetic equation was modified to incorporate the plug flow behavior of biofilters, and used in evaluating the pseudo-kinetic parameters, V-max (the maximum removal rate) and K-m (the half saturation concentration), for hydrogen sulfide biodegradation, and the type of macrokinetic competition between hydrogen sulfide and the organo-sulfur compounds. No significant differences in V-max for the three biofilters were observed. The V-max ranged between 136 and 147 gm(-3) h(-1), while the K-m varied from 44 to 59 ppmv for the three biofilters. Hydrogen sulfide elimination capacity was not affected by the presence of any of the organo-sulfur species in all of the three biofilters. confirming earlier results that hydrogen sulfide removal in biofilters is independent of the presence of organo-sulfur compounds mainly because of its easy biodegradability.