In 1992 we started work on an alternative way of detecting pesticide residues, based on the application of medical immunodiagnostic tests. This type of technology was introduced to the cotton industry last year, through the Lepton (R) test for Heliothis speciation. Immunoassays use antibodies that have been prepared in rabbits, mice or sheep to a particular pesticide. The pesticide molecules are too small to raise an immune response by themselves, so much of the art in developing a pesticide immunoassay consists of coupling a chemical analogue of the pesticide to a carrier, usually a protein that is foreign to the animal being immunized. The analogue must retain all of the characteristic features of the pesticide, but have a new chemical group in its structure that can act as a handle for coupling to the protein. Once coupled to the protein, the pesticide-protein "conjugate" is usually able to evoke antibodies, but for a useful test to be possible, antibodies must be evoked that can bind to the free pesticide, as it would appear in water and other environmental samples.