An indirect enzyme-linked immunosorbent assay (ELISA) for EPTC was developed that may be useful for predicting enhanced carbamothioate herbicide degradation in adapted soils. A modified radioimmunoassay (RIA) procedure was used to detect antibodies specific for EPTC and establish antibody dilutions for optimum ELISA sensitivity. Antibodies were obtained from a rabbit injected with a butylate-analog protein conjugate. An indirect ELISA subsequently was developed for EPTC with a detection range of 10 to 1280 ng ml−1 in a 1:3 aqueous dilution of a 90:10 (v/v) acetonitrile (ACN):water soil extract. EPTC recovery from soil was > 96%, as determined by conventional gas chromatography. Measurement of low concentrations of residual EPTC with the ELISA was less quantitative than by gas chromatography, but the immunoassay provided a rapid, potentially cost-effective method for screening soils to determine enhanced carbamothioate degradation.