WOOD et al.1 demonstrated that the mercury from inorganic chemicals can be methylated by aquatic organisms and also, enzymatically, by extracts of methanogenic bacteria. Since the organic forms of mercury are reported to be more biologically available, these methylation processes in aquatic or sedimentary environments, together with the tendency of methylated mercury to accumulate in biota, are a major reason for bioconcentration of mercury in fish and other organisms found in lakes, streams and bodies of seawater that are contaminated with mercury. As methanogenic bacteria also occur in terrestrial environments, we have investigated possible organo-mercury compound formation in soils contaminated with an inorganic mercury compound.