Contamination of ground water with halogenated aliphatic hydrocarbons threatens the source of drinking water. To study microbial processes that may enhance the removal of these compounds, Lincoln fine sand was exposed to an atmosphere containing methane (4%) to enrich microorganisms capable of growth on the gaseous hydrocarbon. Removal of dichloromethane, trans-1,2-dichloroethylene, chloroform, 1,2-dichloroethane, trichloroethylene, and 1,1,1-trichloroethane was significantly different in methane-enriched soil compared to non-enriched soil (ANOVA, 95% significance level). Tetrachloroethylene was not removed. Autoclaving the methane-enriched soil inhibited completely the removal of all the compounds. These results suggest that methane stimulation of microbial communities may be an alternative treatment technology for bioremediation of contaminated subsurface soils and ground water. (Copyright (c) Federation of European Microbiological Societies 1988.)