Two sources of finished compost material were examined for the capacity to support trichloroethylene(TCE)-degrading microbial populations in a gas-phase bioreactor. Gaseous hydrocarbon was passed through the bioreactor to stimulate cometabolic oxidation of TCE. Significant differences in TCE removal efficiencies were observed between the two compost types, and between hydrocarbon-stimulated and non-stimulated compost. At an average column retention time of 5.6 min, deciduous leaf debris compost removed more than 95% of a 5-50 ppm (by vol.) TCE gas stream, whereas less than 15% removal was observed under similar conditions with a woodchip and bark compost. Trichloroethylene removal efficiency varied with the hydrocarbon-stimulation regime employed, although propane and methane stimulated TCE degradation equally well. Amendment of compost with granular activated carbon substantially increased biological TCE removal. Differences in TCE removal efficiencies observed between the two compost types and between hydrocarbon-stimulated and non-stimulated composts were investigated in terms of changes in the overall heterotrophic microbial populations by using community-level physiological profile analysis.