A competitive enzyme-linked immunosorbent assay (ELISA) for the quantitation of the free paraquat cation was developed using polyclonal rabbit anti-paraquat antibodies bound to a magnetic particle solid phase. A method for the extraction of the paraquat cation from various fruits and vegetables in less than 30 min was developed for use in conjunction with the immunoassay. The procedure has an estimated detection limit of 10 ng/g (ppb) paraquat cation based on the 20 pg/mL estimate in buffer. Results can be easily converted to the dichloride result by dividing the cation concentration by 0.724. Paraquat cation recoveries averaged 99% using this extraction method and immunoassay for cabbage, apples, and potatoes. A collaborative study in which paraquat-fortified zucchini samples were extracted using the traditional 5 h reflux prior to spectrophotometric and immunoassay measurement yielded a correlation of 0.994 with a slope of 1.05