Ethylenebisdithiocarbamate (EBDC) fungicides are the most important class of organic fungicides and exhibit a high degree of carcinogenicity, mutagenicity, and neurotoxicity. For that reason, the safe application of these fungicides in practice requires a convenient method for their determination, applicable to biological fluids. We describe a high-performance liquid chromatography (HPLC) assay. After elimination of the metal which defines the product (maneb, mancozeb, zineb.) with EDTA, the resulting EBDC is derivatized with 1,2-benzenedithiol to yield a cyclocondensation product, 1,3-benzodithiole-2-thione, which can then be quantitated by reversed-phase HPLC at 365 nm using a microBondapak C18 column. The mobile phase was methanol/H2O (70:30, v/v). The assay was linear from 0.25 to 100 microg/mL. Within- and between-day precision and accuracy for this assay were better than 9% and 6%, respectively. The lower limits of detection and quantitation were estimated to be 0.1 and 0.25 microg/mL, respectively. This simple new method has been applied to determine mancozeb concentration in rat urine samples from urinary excretion studies.