A field screening method for the determination of elemental mercury in environmental soil samples involves the thermal desorption of the mercury from the sample onto gold and then the thermal desorption from the gold to a goldfilm mercury vapor analyzer. This field screening method contains a large number of conditions that could be optimized for the various types of soils encountered. In this study, the conditions were optimized for the determination *To whom correspondence should be addressed. 1665This document is a U.S. government work and is not subject to copyright in the United States. EASTERLING, HOVANITZ, AND STREETof mercury in silty clay materials, and the results were comparable to the coldvapor atomic absorption spectrophotometric method of determination. This paper discusses the benefits and disadvantages of employing the field screening method and provides the sequence of conditions that must be optimized to employ this method of determination on other soil types.