This paper highlights some of the difficulties encountered in the production and characterization of beta‐type anti‐idiotype antibodies to haptenic molecules. It describes the techniques employed to overcome these problems and illustrates the importance of the screening assay format in selecting the desired antibodies. The anti‐idiotype antibodies produced were used in a variety of assay formats, some innovative, for the quantification of the pesticides paraquat and phenoxybenzoic acid (PBA). The most sensitive of these assays detected 100 pm ml‐1paraquat and 100 ng ml‐1PBA respectively. The application of these antibodies to multi‐residue tests which overcome the narrow specificity conferred by conventional immunoassay techniques is discussed.