Anti-paraquat antisera were produced by repeated immunization in rabbits with 1-methyl,1'-hexanoic acid-4,4'-bipyridinium (MHBP) coupled to bovine serum albumin (BSA). Less than 0.5 ng of paraquat dichloride was detectable by this assay system. These antisera were strongly cross-reactive with the bipyridyl ring and methyl group in either the 1- or 1'-position of paraquat. The determination of paraquat in tissues of paraquat-poisoned cadavers was also carried out. (Author abstract)