An enzyme-linked immunosorbent assay (ELISA) specific for DDE [1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene] has been used to map DDT [1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane)] residues in the top 10 cm of soil in three river valleys of northern New South Wales, Australia. Despite being almost 20 years since DDT was last applied for cotton growing in these areas, the relationship between sites of greatest application and current residue levels was strong. DDE concentrations in the range 0-2 ppm were found, although most the 389 soil samples examined contained less than 0.2 ppm of DDE. Although some relationship between mode of land use and current residue levels was apparent, this varied from valley to valley and may have reflected different farming practices and times of application. The study demonstrates that the combination of ELISA and geographical information system (GIS) analysis provides an effective means of displaying levels of soil contamination by a pesticide and the possible need for remediation.